diff --git a/CHANGELOG.md b/CHANGELOG.md
index 59a349e..18b7995 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Translation: updated Swedish translation (@eson57)
 - Dialog: prompt only once if several files needs to be reloaded (@yuriiz)
+- Use GTK3's Gtk.Application/Gtk.ApplicationWindow (@yuriiz)
 
 ### Fixed
 
diff --git a/po/diffuse.pot b/po/diffuse.pot
index bed1b36..48a0c8e 100644
--- a/po/diffuse.pot
+++ b/po/diffuse.pot
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2022-10-23 20:00-0400\n"
+"POT-Creation-Date: 2022-11-14 16:24-0500\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -42,604 +42,656 @@ msgstr ""
 msgid "Copyright"
 msgstr ""
 
-#: src/diffuse/dialogs.py:40
+#: src/diffuse/dialogs.py:41
 msgid "Diffuse is a graphical tool for merging and comparing text files."
 msgstr ""
 
-#: src/diffuse/dialogs.py:45
+#: src/diffuse/dialogs.py:46
 msgid "translator-credits"
 msgstr ""
 
-#: src/diffuse/dialogs.py:82
+#: src/diffuse/dialogs.py:83
 msgid "Encoding: "
 msgstr ""
 
-#: src/diffuse/dialogs.py:94
+#: src/diffuse/dialogs.py:95
 msgid "Revision: "
 msgstr ""
 
-#: src/diffuse/dialogs.py:156
+#: src/diffuse/dialogs.py:163
 msgid "Find..."
 msgstr ""
 
-#: src/diffuse/dialogs.py:164
+#: src/diffuse/dialogs.py:173
 msgid "Search For: "
 msgstr ""
 
-#: src/diffuse/dialogs.py:189
+#: src/diffuse/dialogs.py:198
 msgid "Match Case"
 msgstr ""
 
-#: src/diffuse/dialogs.py:194
+#: src/diffuse/dialogs.py:203
 msgid "Search Backwards"
 msgstr ""
 
-#: src/diffuse/main.py:85
+#: src/diffuse/main.py:84
 msgid "Close Tab"
 msgstr ""
 
-#: src/diffuse/main.py:132
+#: src/diffuse/main.py:131
 msgid "Open File..."
 msgstr ""
 
-#: src/diffuse/main.py:133
+#: src/diffuse/main.py:132
 msgid "Reload File"
 msgstr ""
 
-#: src/diffuse/main.py:134
+#: src/diffuse/main.py:133
 msgid "Save File"
 msgstr ""
 
-#: src/diffuse/main.py:135
+#: src/diffuse/main.py:134
 msgid "Save File As..."
 msgstr ""
 
-#: src/diffuse/main.py:217
+#: src/diffuse/main.py:229
 #, python-format
 msgid "Column %d"
 msgstr ""
 
-#: src/diffuse/main.py:291
+#: src/diffuse/main.py:303
 msgid "Save changes before loading the new file?"
 msgstr ""
 
-#: src/diffuse/main.py:402
+#: src/diffuse/main.py:414
 #, python-format
 msgid "Error reading revision %(rev)s of %(file)s."
 msgstr ""
 
-#: src/diffuse/main.py:405 src/diffuse/main.py:1860
+#: src/diffuse/main.py:417 src/diffuse/main.py:2004
 #, python-format
 msgid "Error reading %s."
 msgstr ""
 
-#: src/diffuse/main.py:427
+#: src/diffuse/main.py:439
 msgid "Open File"
 msgstr ""
 
-#: src/diffuse/main.py:484
-#, python-format
-msgid "The file %s changed on disk. Do you want to reload the file?"
-msgstr ""
-
-#: src/diffuse/main.py:510
+#: src/diffuse/main.py:492
 #, python-format
 msgid "Save %(title)s Pane %(pane)d"
 msgstr ""
 
-#: src/diffuse/main.py:542
+#: src/diffuse/main.py:524
 #, python-format
 msgid "A file named %s already exists. Do you want to overwrite it?"
 msgstr ""
 
-#: src/diffuse/main.py:549
+#: src/diffuse/main.py:531
 #, python-format
 msgid ""
 "The file %s has been modified by another process since reading it. If you save, "
 "all the external changes could be lost. Save anyways?"
 msgstr ""
 
-#: src/diffuse/main.py:591
+#: src/diffuse/main.py:573
 #, python-format
 msgid "Error encoding to %s."
 msgstr ""
 
-#: src/diffuse/main.py:595 src/diffuse/preferences.py:300
+#: src/diffuse/main.py:577 src/diffuse/preferences.py:300
 #, python-format
 msgid "Error writing %s."
 msgstr ""
 
-#: src/diffuse/main.py:625
+#: src/diffuse/main.py:607
 msgid "Go To Line..."
 msgstr ""
 
-#: src/diffuse/main.py:626
+#: src/diffuse/main.py:608
 msgid "Line Number: "
 msgstr ""
 
-#: src/diffuse/main.py:657
+#: src/diffuse/main.py:639
 msgid ""
 "Press the enter key or double click to edit. Press the space bar or use the RMB "
 "menu to manually align."
 msgstr ""
 
-#: src/diffuse/main.py:661
+#: src/diffuse/main.py:643
 msgid "Press the escape key to finish editing."
 msgstr ""
 
-#: src/diffuse/main.py:664
+#: src/diffuse/main.py:646
 msgid ""
 "Select target line and press the space bar to align. Press the escape key to "
 "cancel."
 msgstr ""
 
-#: src/diffuse/main.py:787
+#: src/diffuse/main.py:768
 msgid "_File"
 msgstr ""
 
-#: src/diffuse/main.py:788
+#: src/diffuse/main.py:770
 msgid "_Open File..."
 msgstr ""
 
-#: src/diffuse/main.py:789
+#: src/diffuse/main.py:771
 msgid "Open File In New _Tab..."
 msgstr ""
 
-#: src/diffuse/main.py:790
+#: src/diffuse/main.py:772
 msgid "Open _Modified Files..."
 msgstr ""
 
-#: src/diffuse/main.py:791
+#: src/diffuse/main.py:773
 msgid "Open Commi_t..."
 msgstr ""
 
-#: src/diffuse/main.py:792
+#: src/diffuse/main.py:774
 msgid "_Reload File"
 msgstr ""
 
-#: src/diffuse/main.py:794
+#: src/diffuse/main.py:776
 msgid "_Save File"
 msgstr ""
 
-#: src/diffuse/main.py:795
+#: src/diffuse/main.py:777
 msgid "Save File _As..."
 msgstr ""
 
-#: src/diffuse/main.py:796
+#: src/diffuse/main.py:778
 msgid "Save A_ll"
 msgstr ""
 
-#: src/diffuse/main.py:798
+#: src/diffuse/main.py:780
 msgid "New _2-Way File Merge"
 msgstr ""
 
-#: src/diffuse/main.py:799
+#: src/diffuse/main.py:781
 msgid "New _3-Way File Merge"
 msgstr ""
 
-#: src/diffuse/main.py:800
+#: src/diffuse/main.py:782
 msgid "New _N-Way File Merge..."
 msgstr ""
 
-#: src/diffuse/main.py:802
+#: src/diffuse/main.py:784
 msgid "_Close Tab"
 msgstr ""
 
-#: src/diffuse/main.py:803
+#: src/diffuse/main.py:785
 msgid "_Undo Close Tab"
 msgstr ""
 
-#: src/diffuse/main.py:804
+#: src/diffuse/main.py:786
 msgid "_Quit"
 msgstr ""
 
-#: src/diffuse/main.py:807
+#: src/diffuse/main.py:790
 msgid "_Edit"
 msgstr ""
 
-#: src/diffuse/main.py:808
+#: src/diffuse/main.py:792
 msgid "_Undo"
 msgstr ""
 
-#: src/diffuse/main.py:809
+#: src/diffuse/main.py:793
 msgid "_Redo"
 msgstr ""
 
-#: src/diffuse/main.py:811
+#: src/diffuse/main.py:795
 msgid "Cu_t"
 msgstr ""
 
-#: src/diffuse/main.py:812
+#: src/diffuse/main.py:796
 msgid "_Copy"
 msgstr ""
 
-#: src/diffuse/main.py:813
+#: src/diffuse/main.py:797
 msgid "_Paste"
 msgstr ""
 
-#: src/diffuse/main.py:815
+#: src/diffuse/main.py:799
 msgid "Select _All"
 msgstr ""
 
-#: src/diffuse/main.py:816
+#: src/diffuse/main.py:800
 msgid "C_lear Edits"
 msgstr ""
 
-#: src/diffuse/main.py:817
+#: src/diffuse/main.py:801
 msgid "_Dismiss All Edits"
 msgstr ""
 
-#: src/diffuse/main.py:819
+#: src/diffuse/main.py:803
 msgid "_Find..."
 msgstr ""
 
-#: src/diffuse/main.py:820
+#: src/diffuse/main.py:804
 msgid "Find _Next"
 msgstr ""
 
-#: src/diffuse/main.py:821
+#: src/diffuse/main.py:805
 msgid "Find Pre_vious"
 msgstr ""
 
-#: src/diffuse/main.py:822
+#: src/diffuse/main.py:806
 msgid "_Go To Line..."
 msgstr ""
 
-#: src/diffuse/main.py:824
+#: src/diffuse/main.py:808
 msgid "Pr_eferences..."
 msgstr ""
 
-#: src/diffuse/main.py:828
+#: src/diffuse/main.py:812
 msgid "None"
 msgstr ""
 
-#: src/diffuse/main.py:846
+#: src/diffuse/main.py:834
 msgid "_View"
 msgstr ""
 
-#: src/diffuse/main.py:847
+#: src/diffuse/main.py:836
 msgid "_Syntax Highlighting"
 msgstr ""
 
-#: src/diffuse/main.py:849
+#: src/diffuse/main.py:838
 msgid "Re_align All"
 msgstr ""
 
-#: src/diffuse/main.py:850
+#: src/diffuse/main.py:839
 msgid "_Isolate"
 msgstr ""
 
-#: src/diffuse/main.py:852
+#: src/diffuse/main.py:841
 msgid "_First Difference"
 msgstr ""
 
-#: src/diffuse/main.py:853
+#: src/diffuse/main.py:842
 msgid "_Previous Difference"
 msgstr ""
 
-#: src/diffuse/main.py:854
+#: src/diffuse/main.py:843
 msgid "_Next Difference"
 msgstr ""
 
-#: src/diffuse/main.py:855
+#: src/diffuse/main.py:844
 msgid "_Last Difference"
 msgstr ""
 
-#: src/diffuse/main.py:857
+#: src/diffuse/main.py:846
 msgid "Fir_st Tab"
 msgstr ""
 
-#: src/diffuse/main.py:858
+#: src/diffuse/main.py:847
 msgid "Pre_vious Tab"
 msgstr ""
 
-#: src/diffuse/main.py:859
+#: src/diffuse/main.py:848
 msgid "Next _Tab"
 msgstr ""
 
-#: src/diffuse/main.py:860
+#: src/diffuse/main.py:849
 msgid "Las_t Tab"
 msgstr ""
 
-#: src/diffuse/main.py:862
+#: src/diffuse/main.py:851
 msgid "Shift Pane _Right"
 msgstr ""
 
-#: src/diffuse/main.py:863
+#: src/diffuse/main.py:852
 msgid "Shift Pane _Left"
 msgstr ""
 
-#: src/diffuse/main.py:866
+#: src/diffuse/main.py:856
 msgid "F_ormat"
 msgstr ""
 
-#: src/diffuse/main.py:867
+#: src/diffuse/main.py:858
 msgid "Convert To _Upper Case"
 msgstr ""
 
-#: src/diffuse/main.py:868
+#: src/diffuse/main.py:859
 msgid "Convert To _Lower Case"
 msgstr ""
 
-#: src/diffuse/main.py:870
+#: src/diffuse/main.py:861
 msgid "Sort Lines In _Ascending Order"
 msgstr ""
 
-#: src/diffuse/main.py:871
+#: src/diffuse/main.py:862
 msgid "Sort Lines In D_escending Order"
 msgstr ""
 
-#: src/diffuse/main.py:873
+#: src/diffuse/main.py:864
 msgid "Remove Trailing _White Space"
 msgstr ""
 
-#: src/diffuse/main.py:874
+#: src/diffuse/main.py:865
 msgid "Convert Tabs To _Spaces"
 msgstr ""
 
-#: src/diffuse/main.py:875
+#: src/diffuse/main.py:866
 msgid "Convert Leading Spaces To _Tabs"
 msgstr ""
 
-#: src/diffuse/main.py:877
+#: src/diffuse/main.py:868
 msgid "_Increase Indenting"
 msgstr ""
 
-#: src/diffuse/main.py:878
+#: src/diffuse/main.py:869
 msgid "De_crease Indenting"
 msgstr ""
 
-#: src/diffuse/main.py:880
+#: src/diffuse/main.py:871
 msgid "Convert To _DOS Format"
 msgstr ""
 
-#: src/diffuse/main.py:881
+#: src/diffuse/main.py:872
 msgid "Convert To _Mac Format"
 msgstr ""
 
-#: src/diffuse/main.py:882
+#: src/diffuse/main.py:873
 msgid "Convert To Uni_x Format"
 msgstr ""
 
-#: src/diffuse/main.py:885
+#: src/diffuse/main.py:877
 msgid "_Merge"
 msgstr ""
 
-#: src/diffuse/main.py:886
+#: src/diffuse/main.py:879
 msgid "Copy Selection _Right"
 msgstr ""
 
-#: src/diffuse/main.py:887
+#: src/diffuse/main.py:880
 msgid "Copy Selection _Left"
 msgstr ""
 
-#: src/diffuse/main.py:889
+#: src/diffuse/main.py:882
 msgid "Copy Left _Into Selection"
 msgstr ""
 
-#: src/diffuse/main.py:890
+#: src/diffuse/main.py:883
 msgid "Copy Right I_nto Selection"
 msgstr ""
 
-#: src/diffuse/main.py:891
+#: src/diffuse/main.py:884
 msgid "_Merge From Left Then Right"
 msgstr ""
 
-#: src/diffuse/main.py:892
+#: src/diffuse/main.py:885
 msgid "M_erge From Right Then Left"
 msgstr ""
 
-#: src/diffuse/main.py:895
+#: src/diffuse/main.py:889
 msgid "_Help"
 msgstr ""
 
-#: src/diffuse/main.py:896
+#: src/diffuse/main.py:891
 msgid "_Help Contents..."
 msgstr ""
 
-#: src/diffuse/main.py:898
+#: src/diffuse/main.py:893
 #, python-format
 msgid "_About %s..."
 msgstr ""
 
-#: src/diffuse/main.py:913
+#: src/diffuse/main.py:908
 msgid "New 2-Way File Merge"
 msgstr ""
 
-#: src/diffuse/main.py:914
+#: src/diffuse/main.py:909
 msgid "New 3-Way File Merge"
 msgstr ""
 
-#: src/diffuse/main.py:916
+#: src/diffuse/main.py:911
 msgid "Realign All"
 msgstr ""
 
-#: src/diffuse/main.py:917
+#: src/diffuse/main.py:912
 msgid "First Difference"
 msgstr ""
 
-#: src/diffuse/main.py:918
+#: src/diffuse/main.py:913
 msgid "Previous Difference"
 msgstr ""
 
-#: src/diffuse/main.py:919
+#: src/diffuse/main.py:914
 msgid "Next Difference"
 msgstr ""
 
-#: src/diffuse/main.py:920
+#: src/diffuse/main.py:915
 msgid "Last Difference"
 msgstr ""
 
-#: src/diffuse/main.py:922
+#: src/diffuse/main.py:917
 msgid "Copy Selection Right"
 msgstr ""
 
-#: src/diffuse/main.py:923
+#: src/diffuse/main.py:918
 msgid "Copy Selection Left"
 msgstr ""
 
-#: src/diffuse/main.py:924
+#: src/diffuse/main.py:919
 msgid "Copy Left Into Selection"
 msgstr ""
 
-#: src/diffuse/main.py:925
+#: src/diffuse/main.py:920
 msgid "Copy Right Into Selection"
 msgstr ""
 
-#: src/diffuse/main.py:926
+#: src/diffuse/main.py:921
 msgid "Merge From Left Then Right"
 msgstr ""
 
-#: src/diffuse/main.py:927
+#: src/diffuse/main.py:922
 msgid "Merge From Right Then Left"
 msgstr ""
 
-#: src/diffuse/main.py:929
+#: src/diffuse/main.py:924
 msgid "Undo"
 msgstr ""
 
-#: src/diffuse/main.py:930
+#: src/diffuse/main.py:925
 msgid "Redo"
 msgstr ""
 
-#: src/diffuse/main.py:931 src/diffuse/widgets.py:1861
+#: src/diffuse/main.py:926 src/diffuse/widgets.py:1861
 msgid "Cut"
 msgstr ""
 
-#: src/diffuse/main.py:932 src/diffuse/widgets.py:1862
+#: src/diffuse/main.py:927 src/diffuse/widgets.py:1862
 msgid "Copy"
 msgstr ""
 
-#: src/diffuse/main.py:933 src/diffuse/widgets.py:1863
+#: src/diffuse/main.py:928 src/diffuse/widgets.py:1863
 msgid "Paste"
 msgstr ""
 
-#: src/diffuse/main.py:934 src/diffuse/widgets.py:1866
+#: src/diffuse/main.py:929 src/diffuse/widgets.py:1866
 msgid "Clear Edits"
 msgstr ""
 
-#: src/diffuse/main.py:1057
+#: src/diffuse/main.py:996
+msgid "Changes detected"
+msgstr ""
+
+#: src/diffuse/main.py:1000
+#, python-format
+msgid ""
+"The file \"%s\" changed on disk.\n"
+"\n"
+"Do you want to reload the file?"
+msgstr ""
+
+#: src/diffuse/main.py:1005
+#, python-format
+msgid ""
+"The following files changed on disk:\n"
+"%s\n"
+"\n"
+"Do you want to reload these files?"
+msgstr ""
+
+#: src/diffuse/main.py:1120
 msgid "Some files have unsaved changes. Select the files to save before closing."
 msgstr ""
 
-#: src/diffuse/main.py:1071
+#: src/diffuse/main.py:1134
 msgid "Tab"
 msgstr ""
 
-#: src/diffuse/main.py:1076
+#: src/diffuse/main.py:1139
 msgid "Pane"
 msgstr ""
 
-#: src/diffuse/main.py:1087
+#: src/diffuse/main.py:1150
 msgid "Close _Without Saving"
 msgstr ""
 
-#: src/diffuse/main.py:1126
+#: src/diffuse/main.py:1189
 #, python-format
 msgid "Closing this tab will quit %s."
 msgstr ""
 
-#: src/diffuse/main.py:1209
+#: src/diffuse/main.py:1266
 #, python-format
 msgid "File Merge %d"
 msgstr ""
 
-#: src/diffuse/main.py:1315
+#: src/diffuse/main.py:1372
 #, python-format
 msgid "Error retrieving commits for %s."
 msgstr ""
 
-#: src/diffuse/main.py:1347
+#: src/diffuse/main.py:1404
 #, python-format
 msgid "Error retrieving modifications for %s."
 msgstr ""
 
-#: src/diffuse/main.py:1380
+#: src/diffuse/main.py:1437
 msgid "Open File In New Tab"
 msgstr ""
 
-#: src/diffuse/main.py:1403
+#: src/diffuse/main.py:1460
 msgid "Choose Folder With Modified Files"
 msgstr ""
 
-#: src/diffuse/main.py:1421
+#: src/diffuse/main.py:1478
 msgid "No modified files found."
 msgstr ""
 
-#: src/diffuse/main.py:1427
+#: src/diffuse/main.py:1484
 msgid "Choose Folder With Commit"
 msgstr ""
 
-#: src/diffuse/main.py:1447
+#: src/diffuse/main.py:1504
 msgid "No committed files found."
 msgstr ""
 
-#: src/diffuse/main.py:1483
+#: src/diffuse/main.py:1540
 msgid "New N-Way File Merge..."
 msgstr ""
 
-#: src/diffuse/main.py:1484
+#: src/diffuse/main.py:1541
 msgid "Number of panes: "
 msgstr ""
 
-#: src/diffuse/main.py:1558
+#: src/diffuse/main.py:1615
 msgid "Phrase not found.  Continue from the end of the file?"
 msgstr ""
 
-#: src/diffuse/main.py:1560
+#: src/diffuse/main.py:1617
 msgid "Phrase not found.  Continue from the start of the file?"
 msgstr ""
 
-#: src/diffuse/main.py:1781
+#: src/diffuse/main.py:1827
+msgid "Do not read any resource files"
+msgstr ""
+
+#: src/diffuse/main.py:1835
+msgid "Specify explicit resource file"
+msgstr ""
+
+#: src/diffuse/main.py:1843
+msgid "File revisions <rev-1> and <rev>"
+msgstr ""
+
+#: src/diffuse/main.py:1851
+msgid "Close all tabs with no differences"
+msgstr ""
+
+#: src/diffuse/main.py:1858
+msgid "Use <codec> to read and write files"
+msgstr ""
+
+#: src/diffuse/main.py:1866
+msgid "Display <label> instead of the file name"
+msgstr ""
+
+#: src/diffuse/main.py:1874
+msgid "Create a new tab for each modified file"
+msgstr ""
+
+#: src/diffuse/main.py:1881
+msgid "File revision <rev>"
+msgstr ""
+
+#: src/diffuse/main.py:1889
+msgid "Create a new tab for each file"
+msgstr ""
+
+#: src/diffuse/main.py:1896
+msgid "Start a new tab"
+msgstr ""
+
+#: src/diffuse/main.py:1903 src/diffuse/preferences.py:165
+msgid "Version control system search order"
+msgstr ""
+
+#: src/diffuse/main.py:1911
+msgid "Start with line <line> selected"
+msgstr ""
+
+#: src/diffuse/main.py:1919
+msgid "Create a blank file comparison pane"
+msgstr ""
+
+#: src/diffuse/main.py:1926 src/diffuse/preferences.py:91
+#: src/diffuse/preferences.py:100
+msgid "Ignore changes to white space"
+msgstr ""
+
+#: src/diffuse/main.py:1933
+msgid "Ignore changes in blank lines"
+msgstr ""
+
+#: src/diffuse/main.py:1940 src/diffuse/preferences.py:93
+msgid "Ignore end of line differences"
+msgstr ""
+
+#: src/diffuse/main.py:1947 src/diffuse/preferences.py:89
+msgid "Ignore case differences"
+msgstr ""
+
+#: src/diffuse/main.py:1954 src/diffuse/preferences.py:90
+msgid "Ignore white space differences"
+msgstr ""
+
+#: src/diffuse/main.py:1957
 msgid ""
-"Usage:\n"
-"    diffuse [OPTION...] [FILE...]\n"
-"    diffuse ( -h | -? | --help | -v | --version )\n"
-"\n"
 "Diffuse is a graphical tool for merging and comparing text files. Diffuse is\n"
 "able to compare an arbitrary number of files side-by-side and gives users the\n"
 "ability to manually adjust line matching and directly edit files. Diffuse can\n"
-"also retrieve revisions of files from several VCSs for comparison and merging.\n"
-"\n"
-"Help Options:\n"
-"  ( -h | -? | --help )             Display this usage information\n"
-"  ( -v | --version )               Display version and copyright information\n"
-"\n"
-"Configuration Options:\n"
-"  --no-rcfile                      Do not read any resource files\n"
-"  --rcfile <file>                  Specify explicit resource file\n"
-"\n"
-"General Options:\n"
-"  ( -c | --commit ) <rev>          File revisions <rev-1> and <rev>\n"
-"  ( -D | --close-if-same )         Close all tabs with no differences\n"
-"  ( -e | --encoding ) <codec>      Use <codec> to read and write files\n"
-"  ( -L | --label ) <label>         Display <label> instead of the file name\n"
-"  ( -m | --modified )              Create a new tab for each modified file\n"
-"  ( -r | --revision ) <rev>        File revision <rev>\n"
-"  ( -s | --separate )              Create a new tab for each file\n"
-"  ( -t | --tab )                   Start a new tab\n"
-"  ( -V | --vcs ) <vcs-list>        Version control system search order\n"
-"  --line <line>                    Start with line <line> selected\n"
-"  --null-file                      Create a blank file comparison pane\n"
-"\n"
-"Display Options:\n"
-"  ( -b | --ignore-space-change )   Ignore changes to white space\n"
-"  ( -B | --ignore-blank-lines )    Ignore changes in blank lines\n"
-"  ( -E | --ignore-end-of-line )    Ignore end of line differences\n"
-"  ( -i | --ignore-case )           Ignore case differences\n"
-"  ( -w | --ignore-all-space )      Ignore white space differences"
+"also retrieve revisions of files from several VCSs for comparison and merging."
 msgstr ""
 
-#: src/diffuse/main.py:1948
+#: src/diffuse/main.py:2080
 msgid "Error parsing line number."
 msgstr ""
 
-#: src/diffuse/main.py:1958
-#, python-format
-msgid "Skipping unknown argument \"%s\"."
-msgstr ""
-
-#: src/diffuse/main.py:1966
+#: src/diffuse/main.py:2096
 #, python-format
 msgid "Error processing argument \"%s\".  Directory not expected."
 msgstr ""
@@ -672,26 +724,10 @@ msgstr ""
 msgid "Show white space characters"
 msgstr ""
 
-#: src/diffuse/preferences.py:89
-msgid "Ignore case differences"
-msgstr ""
-
-#: src/diffuse/preferences.py:90
-msgid "Ignore white space differences"
-msgstr ""
-
-#: src/diffuse/preferences.py:91 src/diffuse/preferences.py:100
-msgid "Ignore changes to white space"
-msgstr ""
-
 #: src/diffuse/preferences.py:92
 msgid "Ignore blank line differences"
 msgstr ""
 
-#: src/diffuse/preferences.py:93
-msgid "Ignore end of line differences"
-msgstr ""
-
 #: src/diffuse/preferences.py:95
 msgid "Alignment"
 msgstr ""
@@ -769,10 +805,6 @@ msgstr ""
 msgid "Cygdrive prefix"
 msgstr ""
 
-#: src/diffuse/preferences.py:165
-msgid "Version control system search order"
-msgstr ""
-
 #: src/diffuse/preferences.py:173
 msgid "\"co\" command"
 msgstr ""
@@ -882,7 +914,7 @@ msgstr ""
 msgid "Unhandled error at line {line} of {file}."
 msgstr ""
 
-#: src/diffuse/utils.py:66
+#: src/diffuse/utils.py:65
 msgid "Auto Detect"
 msgstr ""
 
diff --git a/src/diffuse/main.py b/src/diffuse/main.py
index 24ef668..cd65d1a 100644
--- a/src/diffuse/main.py
+++ b/src/diffuse/main.py
@@ -38,7 +38,6 @@ from diffuse.utils import LineEnding
 from diffuse.vcs.vcs_interface import VcsInterface
 from diffuse.vcs.vcs_registry import VcsRegistry
 from diffuse.widgets import FileDiffViewerBase, EditMode
-from diffuse.widgets import createMenu
 
 import gi  # type: ignore
 gi.require_version('GObject', '2.0')
@@ -47,8 +46,8 @@ gi.require_version('Gdk', '3.0')
 gi.require_version('GdkPixbuf', '2.0')
 gi.require_version('Pango', '1.0')
 gi.require_version('PangoCairo', '1.0')
-from gi.repository import GObject, Gtk, Gdk, GdkPixbuf, Pango  # type: ignore # noqa: E402
-
+from gi.repository import (Gdk, GdkPixbuf, Gio,  # type: ignore # noqa: E402
+                           GLib, GObject, Gtk, Pango)
 
 theVCSs = VcsRegistry()
 
@@ -121,7 +120,7 @@ class FileInfo:
 # the main application class containing a set of file viewers
 # this class displays tab for switching between viewers and dispatches menu
 # commands to the current viewer
-class Diffuse(Gtk.Window):
+class Diffuse(Gtk.ApplicationWindow):
     # specialization of FileDiffViewerBase for Diffuse
     class FileDiffViewer(FileDiffViewerBase):
         # pane header
@@ -665,8 +664,8 @@ class Diffuse(Gtk.Window):
         def format_changed_cb(self, widget, f, fmt):
             self.footers[f].setFormat(fmt)
 
-    def __init__(self, rc_dir):
-        super().__init__(type=Gtk.WindowType.TOPLEVEL)
+    def __init__(self, rc_dir, *args, **kwargs):
+        super().__init__(type=Gtk.WindowType.TOPLEVEL, *args, **kwargs)
 
         self.prefs = Preferences(os.path.join(rc_dir, 'prefs'))
         # number of created viewers (used to label some tabs)
@@ -698,7 +697,6 @@ class Diffuse(Gtk.Window):
         self.search_history: List[str] = []
 
         self.connect('delete-event', self.delete_cb)
-        accel_group = Gtk.AccelGroup()
 
         # create a Box for our contents
         vbox = Gtk.Box(orientation=Gtk.Orientation.VERTICAL)
@@ -717,7 +715,7 @@ class Diffuse(Gtk.Window):
         factory = Gtk.IconFactory()
 
         # render the base item used to indicate a new document
-        p0 = default_theme.load_icon_for_scale("document-new", icon_size, scale_factor, 0)
+        p0 = default_theme.load_icon_for_scale('document-new', icon_size, scale_factor, 0)
         w, h = p0.get_width(), p0.get_height()
 
         # render new 2-way merge icon
@@ -743,8 +741,8 @@ class Diffuse(Gtk.Window):
         factory.add(DIFFUSE_STOCK_NEW_3WAY_MERGE, Gtk.IconSet.new_from_pixbuf(p))
 
         # render the left and right arrow we will use in our custom icons
-        p0 = default_theme.load_icon_for_scale("go-next", icon_size, scale_factor, 0)
-        p1 = default_theme.load_icon_for_scale("go-previous", icon_size, scale_factor, 0)
+        p0 = default_theme.load_icon_for_scale('go-next', icon_size, scale_factor, 0)
+        p1 = default_theme.load_icon_for_scale('go-previous', icon_size, scale_factor, 0)
         w, h, s = p0.get_width(), p0.get_height(), 0.65
         sw, sh = int(s * w), int(s * h)
         w1, h1 = w - sw, h - sh
@@ -768,127 +766,141 @@ class Diffuse(Gtk.Window):
 
         menuspecs = []
         menuspecs.append([_('_File'), [
-            [_('_Open File...'), self.open_file_cb, None, Gtk.STOCK_OPEN, 'open_file'],
-            [_('Open File In New _Tab...'), self.open_file_in_new_tab_cb, None, None, 'open_file_in_new_tab'],  # noqa: E501
-            [_('Open _Modified Files...'), self.open_modified_files_cb, None, None, 'open_modified_files'],  # noqa: E501
-            [_('Open Commi_t...'), self.open_commit_cb, None, None, 'open_commit'],
-            [_('_Reload File'), self.reload_file_cb, None, Gtk.STOCK_REFRESH, 'reload_file'],
-            [],
-            [_('_Save File'), self.save_file_cb, None, Gtk.STOCK_SAVE, 'save_file'],
-            [_('Save File _As...'), self.save_file_as_cb, None, Gtk.STOCK_SAVE_AS, 'save_file_as'],
-            [_('Save A_ll'), self.save_all_cb, None, None, 'save_all'],
-            [],
-            [_('New _2-Way File Merge'), self.new_2_way_file_merge_cb, None, DIFFUSE_STOCK_NEW_2WAY_MERGE, 'new_2_way_file_merge'],  # noqa: E501
-            [_('New _3-Way File Merge'), self.new_3_way_file_merge_cb, None, DIFFUSE_STOCK_NEW_3WAY_MERGE, 'new_3_way_file_merge'],  # noqa: E501
-            [_('New _N-Way File Merge...'), self.new_n_way_file_merge_cb, None, None, 'new_n_way_file_merge'],  # noqa: E501
-            [],
-            [_('_Close Tab'), self.close_tab_cb, None, Gtk.STOCK_CLOSE, 'close_tab'],
-            [_('_Undo Close Tab'), self.undo_close_tab_cb, None, None, 'undo_close_tab'],
-            [_('_Quit'), self.quit_cb, None, Gtk.STOCK_QUIT, 'quit']
+            [
+                [_('_Open File...'), self.open_file_cb, None, 'open_file'],
+                [_('Open File In New _Tab...'), self.open_file_in_new_tab_cb, None, 'open_file_in_new_tab'],  # noqa: E501
+                [_('Open _Modified Files...'), self.open_modified_files_cb, None, 'open_modified_files'],  # noqa: E501
+                [_('Open Commi_t...'), self.open_commit_cb, None, 'open_commit'],
+                [_('_Reload File'), self.reload_file_cb, None, 'reload_file'],
+            ], [
+                [_('_Save File'), self.save_file_cb, None, 'save_file'],
+                [_('Save File _As...'), self.save_file_as_cb, None, 'save_file_as'],
+                [_('Save A_ll'), self.save_all_cb, None, 'save_all'],
+            ], [
+                [_('New _2-Way File Merge'), self.new_2_way_file_merge_cb, None, 'new_2_way_file_merge'],  # noqa: E501
+                [_('New _3-Way File Merge'), self.new_3_way_file_merge_cb, None, 'new_3_way_file_merge'],  # noqa: E501
+                [_('New _N-Way File Merge...'), self.new_n_way_file_merge_cb, None, 'new_n_way_file_merge'],  # noqa: E501
+            ], [
+                [_('_Close Tab'), self.close_tab_cb, None, 'close_tab'],
+                [_('_Undo Close Tab'), self.undo_close_tab_cb, None, 'undo_close_tab'],
+                [_('_Quit'), self.quit_cb, None, 'quit']
+            ]
         ]])
 
         menuspecs.append([_('_Edit'), [
-            [_('_Undo'), self.button_cb, 'undo', Gtk.STOCK_UNDO, 'undo'],
-            [_('_Redo'), self.button_cb, 'redo', Gtk.STOCK_REDO, 'redo'],
-            [],
-            [_('Cu_t'), self.button_cb, 'cut', Gtk.STOCK_CUT, 'cut'],
-            [_('_Copy'), self.button_cb, 'copy', Gtk.STOCK_COPY, 'copy'],
-            [_('_Paste'), self.button_cb, 'paste', Gtk.STOCK_PASTE, 'paste'],
-            [],
-            [_('Select _All'), self.button_cb, 'select_all', None, 'select_all'],
-            [_('C_lear Edits'), self.button_cb, 'clear_edits', Gtk.STOCK_CLEAR, 'clear_edits'],
-            [_('_Dismiss All Edits'), self.button_cb, 'dismiss_all_edits', None, 'dismiss_all_edits'],  # noqa: E501
-            [],
-            [_('_Find...'), self.find_cb, None, Gtk.STOCK_FIND, 'find'],
-            [_('Find _Next'), self.find_next_cb, None, None, 'find_next'],
-            [_('Find Pre_vious'), self.find_previous_cb, None, None, 'find_previous'],
-            [_('_Go To Line...'), self.go_to_line_cb, None, Gtk.STOCK_JUMP_TO, 'go_to_line'],
-            [],
-            [_('Pr_eferences...'), self.preferences_cb, None, Gtk.STOCK_PREFERENCES, 'preferences']
+            [
+                [_('_Undo'), self.button_cb, 'undo', 'undo'],
+                [_('_Redo'), self.button_cb, 'redo', 'redo'],
+            ], [
+                [_('Cu_t'), self.button_cb, 'cut', 'cut'],
+                [_('_Copy'), self.button_cb, 'copy', 'copy'],
+                [_('_Paste'), self.button_cb, 'paste', 'paste'],
+            ], [
+                [_('Select _All'), self.button_cb, 'select_all', 'select_all'],
+                [_('C_lear Edits'), self.button_cb, 'clear_edits', 'clear_edits'],
+                [_('_Dismiss All Edits'), self.button_cb, 'dismiss_all_edits', 'dismiss_all_edits'],
+            ], [
+                [_('_Find...'), self.find_cb, None, 'find'],
+                [_('Find _Next'), self.find_next_cb, None, 'find_next'],
+                [_('Find Pre_vious'), self.find_previous_cb, None, 'find_previous'],
+                [_('_Go To Line...'), self.go_to_line_cb, None, 'go_to_line'],
+            ], [
+                [_('Pr_eferences...'), self.preferences_cb, None, 'preferences']
+            ]
         ]])
 
-        submenudef = [
-            [_('None'), self.syntax_cb, None, None, 'no_syntax_highlighting', True, None, ('syntax', None)]  # noqa: E501
-        ]
+        syntax_menu = [[[_('None'), None, '', 'syntax_highlighting']]]
         names = theResources.getSyntaxNames()
+        variant = GLib.Variant.new_string('')
+        self.syntax_action = Gio.SimpleAction.new_stateful(
+            'syntax_highlighting', variant.get_type(), variant
+        )
+        self.syntax_action.connect('change-state', self.syntax_cb)
+        self.add_action(self.syntax_action)
         if len(names) > 0:
-            submenudef.append([])
+            syntax_section = []
             names.sort(key=str.lower)
             for name in names:
-                submenudef.append([
-                    name,
-                    self.syntax_cb,
-                    name,
-                    None,
-                    'syntax_highlighting_' + name,
-                    True,
-                    None,
-                    ('syntax', name)
-                ])
+                syntax_section.append(
+                    [
+                        name,
+                        None,
+                        name,
+                        'syntax_highlighting',
+                    ]
+                )
+            syntax_menu.append(syntax_section)
 
         menuspecs.append([_('_View'), [
-            [_('_Syntax Highlighting'), None, None, None, None, True, submenudef],
-            [],
-            [_('Re_align All'), self.button_cb, 'realign_all', Gtk.STOCK_EXECUTE, 'realign_all'],
-            [_('_Isolate'), self.button_cb, 'isolate', None, 'isolate'],
-            [],
-            [_('_First Difference'), self.button_cb, 'first_difference', Gtk.STOCK_GOTO_TOP, 'first_difference'],  # noqa: E501
-            [_('_Previous Difference'), self.button_cb, 'previous_difference', Gtk.STOCK_GO_UP, 'previous_difference'],  # noqa: E501
-            [_('_Next Difference'), self.button_cb, 'next_difference', Gtk.STOCK_GO_DOWN, 'next_difference'],  # noqa: E501
-            [_('_Last Difference'), self.button_cb, 'last_difference', Gtk.STOCK_GOTO_BOTTOM, 'last_difference'],  # noqa: E501
-            [],
-            [_('Fir_st Tab'), self.first_tab_cb, None, None, 'first_tab'],
-            [_('Pre_vious Tab'), self.previous_tab_cb, None, None, 'previous_tab'],
-            [_('Next _Tab'), self.next_tab_cb, None, None, 'next_tab'],
-            [_('Las_t Tab'), self.last_tab_cb, None, None, 'last_tab'],
-            [],
-            [_('Shift Pane _Right'), self.button_cb, 'shift_pane_right', None, 'shift_pane_right'],
-            [_('Shift Pane _Left'), self.button_cb, 'shift_pane_left', None, 'shift_pane_left']
+            [
+                [_('_Syntax Highlighting'), None, None, None, syntax_menu]
+            ], [
+                [_('Re_align All'), self.button_cb, 'realign_all', 'realign_all'],
+                [_('_Isolate'), self.button_cb, 'isolate', 'isolate'],
+            ], [
+                [_('_First Difference'), self.button_cb, 'first_difference', 'first_difference'],
+                [_('_Previous Difference'), self.button_cb, 'previous_difference', 'previous_difference'],  # noqa: E501
+                [_('_Next Difference'), self.button_cb, 'next_difference', 'next_difference'],
+                [_('_Last Difference'), self.button_cb, 'last_difference', 'last_difference'],
+            ], [
+                [_('Fir_st Tab'), self.first_tab_cb, None, 'first_tab'],
+                [_('Pre_vious Tab'), self.previous_tab_cb, None, 'previous_tab'],
+                [_('Next _Tab'), self.next_tab_cb, None, 'next_tab'],
+                [_('Las_t Tab'), self.last_tab_cb, None, 'last_tab'],
+            ], [
+                [_('Shift Pane _Right'), self.button_cb, 'shift_pane_right', 'shift_pane_right'],
+                [_('Shift Pane _Left'), self.button_cb, 'shift_pane_left', 'shift_pane_left']
+            ]
         ]])
 
         menuspecs.append([_('F_ormat'), [
-            [_('Convert To _Upper Case'), self.button_cb, 'convert_to_upper_case', None, 'convert_to_upper_case'],  # noqa: E501
-            [_('Convert To _Lower Case'), self.button_cb, 'convert_to_lower_case', None, 'convert_to_lower_case'],  # noqa: E501
-            [],
-            [_('Sort Lines In _Ascending Order'), self.button_cb, 'sort_lines_in_ascending_order', Gtk.STOCK_SORT_ASCENDING, 'sort_lines_in_ascending_order'],  # noqa: E501
-            [_('Sort Lines In D_escending Order'), self.button_cb, 'sort_lines_in_descending_order', Gtk.STOCK_SORT_DESCENDING, 'sort_lines_in_descending_order'],  # noqa: E501
-            [],
-            [_('Remove Trailing _White Space'), self.button_cb, 'remove_trailing_white_space', None, 'remove_trailing_white_space'],  # noqa: E501
-            [_('Convert Tabs To _Spaces'), self.button_cb, 'convert_tabs_to_spaces', None, 'convert_tabs_to_spaces'],  # noqa: E501
-            [_('Convert Leading Spaces To _Tabs'), self.button_cb, 'convert_leading_spaces_to_tabs', None, 'convert_leading_spaces_to_tabs'],  # noqa: E501
-            [],
-            [_('_Increase Indenting'), self.button_cb, 'increase_indenting', Gtk.STOCK_INDENT, 'increase_indenting'],  # noqa: E501
-            [_('De_crease Indenting'), self.button_cb, 'decrease_indenting', Gtk.STOCK_UNINDENT, 'decrease_indenting'],  # noqa: E501
-            [],
-            [_('Convert To _DOS Format'), self.button_cb, 'convert_to_dos', None, 'convert_to_dos'],  # noqa: E501
-            [_('Convert To _Mac Format'), self.button_cb, 'convert_to_mac', None, 'convert_to_mac'],  # noqa: E501
-            [_('Convert To Uni_x Format'), self.button_cb, 'convert_to_unix', None, 'convert_to_unix']  # noqa: E501
+            [
+                [_('Convert To _Upper Case'), self.button_cb, 'convert_to_upper_case', 'convert_to_upper_case'],  # noqa: E501
+                [_('Convert To _Lower Case'), self.button_cb, 'convert_to_lower_case', 'convert_to_lower_case'],  # noqa: E501
+            ], [
+                [_('Sort Lines In _Ascending Order'), self.button_cb, 'sort_lines_in_ascending_order', 'sort_lines_in_ascending_order'],  # noqa: E501
+                [_('Sort Lines In D_escending Order'), self.button_cb, 'sort_lines_in_descending_order', 'sort_lines_in_descending_order'],  # noqa: E501
+            ], [
+                [_('Remove Trailing _White Space'), self.button_cb, 'remove_trailing_white_space', 'remove_trailing_white_space'],  # noqa: E501
+                [_('Convert Tabs To _Spaces'), self.button_cb, 'convert_tabs_to_spaces', 'convert_tabs_to_spaces'],  # noqa: E501
+                [_('Convert Leading Spaces To _Tabs'), self.button_cb, 'convert_leading_spaces_to_tabs', 'convert_leading_spaces_to_tabs'],  # noqa: E501
+            ], [
+                [_('_Increase Indenting'), self.button_cb, 'increase_indenting', 'increase_indenting'],  # noqa: E501
+                [_('De_crease Indenting'), self.button_cb, 'decrease_indenting', 'decrease_indenting'],  # noqa: E501
+            ], [
+                [_('Convert To _DOS Format'), self.button_cb, 'convert_to_dos', 'convert_to_dos'],
+                [_('Convert To _Mac Format'), self.button_cb, 'convert_to_mac', 'convert_to_mac'],
+                [_('Convert To Uni_x Format'), self.button_cb, 'convert_to_unix', 'convert_to_unix']
+            ]
         ]])
 
         menuspecs.append([_('_Merge'), [
-            [_('Copy Selection _Right'), self.button_cb, 'copy_selection_right', Gtk.STOCK_GOTO_LAST, 'copy_selection_right'],  # noqa: E501
-            [_('Copy Selection _Left'), self.button_cb, 'copy_selection_left', Gtk.STOCK_GOTO_FIRST, 'copy_selection_left'],  # noqa: E501
-            [],
-            [_('Copy Left _Into Selection'), self.button_cb, 'copy_left_into_selection', Gtk.STOCK_GO_FORWARD, 'copy_left_into_selection'],  # noqa: E501
-            [_('Copy Right I_nto Selection'), self.button_cb, 'copy_right_into_selection', Gtk.STOCK_GO_BACK, 'copy_right_into_selection'],  # noqa: E501
-            [_('_Merge From Left Then Right'), self.button_cb, 'merge_from_left_then_right', DIFFUSE_STOCK_LEFT_RIGHT, 'merge_from_left_then_right'],  # noqa: E501
-            [_('M_erge From Right Then Left'), self.button_cb, 'merge_from_right_then_left', DIFFUSE_STOCK_RIGHT_LEFT, 'merge_from_right_then_left']  # noqa: E501
+            [
+                [_('Copy Selection _Right'), self.button_cb, 'copy_selection_right', 'copy_selection_right'],  # noqa: E501
+                [_('Copy Selection _Left'), self.button_cb, 'copy_selection_left', 'copy_selection_left'],  # noqa: E501
+            ], [
+                [_('Copy Left _Into Selection'), self.button_cb, 'copy_left_into_selection', 'copy_left_into_selection'],  # noqa: E501
+                [_('Copy Right I_nto Selection'), self.button_cb, 'copy_right_into_selection', 'copy_right_into_selection'],  # noqa: E501
+                [_('_Merge From Left Then Right'), self.button_cb, 'merge_from_left_then_right', 'merge_from_left_then_right'],  # noqa: E501
+                [_('M_erge From Right Then Left'), self.button_cb, 'merge_from_right_then_left', 'merge_from_right_then_left']  # noqa: E501
+            ]
         ]])
 
         menuspecs.append([_('_Help'), [
-            [_('_Help Contents...'), self.help_contents_cb, None, Gtk.STOCK_HELP, 'help_contents'],
-            [],
-            [_('_About %s...') % (constants.APP_NAME, ), self.about_cb, None, Gtk.STOCK_ABOUT, 'about']  # noqa: E501
+            [
+                [_('_Help Contents...'), self.help_contents_cb, None, 'help_contents'],
+            ], [
+                [_('_About %s...') % (constants.APP_NAME, ), self.about_cb, None, 'about']
+            ]
         ]])
 
         # used to disable menu events when switching tabs
         self.menu_update_depth = 0
-        # build list of radio menu items so we can update them to match the
-        # currently viewed pane
-        self.radio_menus = radio_menus = {}
-        menu_bar = _create_menu_bar(menuspecs, radio_menus, accel_group)
-        vbox.pack_start(menu_bar, False, False, 0)
-        menu_bar.show()
+
+        menubar = Gio.Menu()
+        for label, sections in menuspecs:
+            menubar.append_submenu(label, self._create_menu(sections))
+        self.get_application().set_menubar(menubar)
 
         # create button bar
         hbox = Gtk.Box(orientation=Gtk.Orientation.HORIZONTAL, spacing=0)
@@ -933,11 +945,39 @@ class Diffuse(Gtk.Window):
         vbox.pack_start(statusbar, False, False, 0)
         statusbar.show()
 
-        self.add_accel_group(accel_group)
         self.add(vbox)
         vbox.show()
         self.connect('focus-in-event', self.focus_in_cb)
 
+    def _create_menu(self, sections):
+        menu = Gio.Menu.new()
+        for section in sections:
+            section_menu = Gio.Menu.new()
+            for label, cb, cb_data, accel, *submenu in section:
+                if submenu:
+                    (submenu,) = submenu
+                    section_menu.append_submenu(label, self._create_menu(submenu))
+                else:
+                    if cb_data is not None:
+                        cb_data = GLib.Variant.new_string(cb_data)
+                    accel = accel.replace('_', '-')
+                    if cb is not None:
+                        action = Gio.SimpleAction.new(accel, cb_data and cb_data.get_type())
+                        action.connect('activate', cb)
+                        self.add_action(action)
+                    item = Gio.MenuItem.new(label)
+                    item.set_action_and_target_value('win.' + accel, cb_data)
+                    key_binding = theResources.getKeyBindings('menu', accel)
+                    if len(key_binding) > 0:
+                        key, modifier = key_binding[0]
+                        self.get_application().set_accels_for_action(
+                            Gio.Action.print_detailed_name('win.' + accel, cb_data),
+                            [Gtk.accelerator_name(key, modifier)],
+                        )
+                    section_menu.append_item(item)
+            menu.append_section(None, section_menu)
+        return menu
+
     # notifies all viewers on focus changes so they may check for external
     # changes to files
     def focus_in_cb(self, widget, event):
@@ -955,18 +995,18 @@ class Diffuse(Gtk.Window):
                 filename = h.info.label if h.info.label is not None else h.info.name
                 filenames.append(filename)
 
-            primary_text = _("Changes detected")
-            secondary_text = ""
+            primary_text = _('Changes detected')
+            secondary_text = ''
             if len(filenames) == 1:
                 secondary_text = _(
-                    "The file \"%s\" changed on disk.\n\n"
-                    "Do you want to reload the file?"
+                    'The file "%s" changed on disk.\n\n'
+                    'Do you want to reload the file?'
                 ) % (filenames[0],)
             else:
                 secondary_text = _(
-                    "The following files changed on disk:\n%s\n\n"
-                    "Do you want to reload these files?"
-                ) % ("\n".join("- " + filename for filename in filenames),)
+                    'The following files changed on disk:\n%s\n\n'
+                    'Do you want to reload these files?'
+                ) % ('\n'.join('- ' + filename for filename in filenames),)
 
             dialog = Gtk.MessageDialog(
                 transient_for=self.get_toplevel(),
@@ -1041,7 +1081,7 @@ class Diffuse(Gtk.Window):
                 ss.append(f'{k} {v}\n')
             ss.sort()
             f = open(statepath, 'w')
-            f.write(f"# This state file was generated by {constants.APP_NAME} {constants.VERSION}.\n\n")  # noqa: E501
+            f.write(f'# This state file was generated by {constants.APP_NAME} {constants.VERSION}.\n\n')  # noqa: E501
             for s in ss:
                 f.write(s)
             f.close()
@@ -1194,13 +1234,7 @@ class Diffuse(Gtk.Window):
     # update the label in the status bar
     def setSyntax(self, s):
         # update menu
-        t = self.radio_menus.get('syntax', None)
-        if t is not None:
-            t = t[1]
-            if s in t:
-                self.menu_update_depth += 1
-                t[s].set_active(True)
-                self.menu_update_depth -= 1
+        self.syntax_action.set_state(GLib.Variant.new_string(s or ''))
 
     # callback used when switching notebook pages
     def switch_page_cb(self, widget, ptr, page_num):
@@ -1387,7 +1421,7 @@ class Diffuse(Gtk.Window):
     # respond to close window request from the window manager
     def delete_cb(self, widget, event):
         if self.confirmQuit():
-            Gtk.main_quit()
+            self.get_application().quit()
             return False
         return True
 
@@ -1534,7 +1568,7 @@ class Diffuse(Gtk.Window):
     # callback for the quit menu item
     def quit_cb(self, widget, data):
         if self.confirmQuit():
-            Gtk.main_quit()
+            self.get_application().quit()
 
     # request search parameters if force=True and then perform a search in the
     # current viewer pane
@@ -1644,7 +1678,7 @@ class Diffuse(Gtk.Window):
 
     # callback for most menu items and buttons
     def button_cb(self, widget, data):
-        self.getCurrentViewer().button_cb(widget, data)
+        self.getCurrentViewer().button_cb(widget, data.get_string())
 
     # display help documentation
     def help_contents_cb(self, widget, data):
@@ -1711,18 +1745,6 @@ class Diffuse(Gtk.Window):
         dialog.destroy()
 
 
-# convenience method for creating a menu bar according to a template
-def _create_menu_bar(specs, radio, accel_group):
-    menu_bar = Gtk.MenuBar()
-    for label, spec in specs:
-        menu = Gtk.MenuItem.new_with_mnemonic(label)
-        menu.set_submenu(createMenu(spec, radio, accel_group))
-        menu.set_use_underline(True)
-        menu.show()
-        menu_bar.append(menu)
-    return menu_bar
-
-
 # convenience method for packing buttons into a container according to a
 # template
 def _append_buttons(box, size, specs):
@@ -1789,207 +1811,305 @@ GObject.signal_new('save', Diffuse.FileDiffViewer.PaneHeader, GObject.SignalFlag
 GObject.signal_new('save-as', Diffuse.FileDiffViewer.PaneHeader, GObject.SignalFlags.RUN_LAST, GObject.TYPE_NONE, ())  # noqa: E501
 
 
-def main(version, sysconfigdir):
-    # app = Application()
-    # return app.run(sys.argv)
+class Application(Gtk.Application):
+    def __init__(self, sysconfigdir, *args, **kwargs):
+        super().__init__(
+            *args,
+            application_id='io.github.mightycreak.Diffuse',
+            flags=Gio.ApplicationFlags.HANDLES_COMMAND_LINE | Gio.ApplicationFlags.NON_UNIQUE,
+            **kwargs,
+        )
 
-    args = sys.argv
-    argc = len(args)
+        self.sysconfigdir = sysconfigdir
 
-    constants.VERSION = version
-
-    if argc == 2 and args[1] in ['-v', '--version']:
-        print('%s %s\n%s' % (constants.APP_NAME, constants.VERSION, constants.COPYRIGHT))
-        return 0
-
-    if argc == 2 and args[1] in ['-h', '-?', '--help']:
-        print(_('''Usage:
-    diffuse [OPTION...] [FILE...]
-    diffuse ( -h | -? | --help | -v | --version )
-
-Diffuse is a graphical tool for merging and comparing text files. Diffuse is
+        self.add_main_option(
+            'version',
+            ord('v'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Display version and copyright information'),
+            None,
+        )
+        self.add_main_option(
+            'no-rcfile',
+            0,
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Do not read any resource files'),
+            None,
+        )
+        self.add_main_option(
+            'rcfile',
+            0,
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.STRING,
+            _('Specify explicit resource file'),
+            'file',
+        )
+        self.add_main_option(
+            'commit',
+            ord('c'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.STRING,
+            _('File revisions <rev-1> and <rev>'),
+            'rev',
+        )
+        self.add_main_option(
+            'close-if-same',
+            ord('D'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Close all tabs with no differences'),
+        )
+        self.add_main_option(
+            'encoding',
+            ord('e'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.STRING,
+            _('Use <codec> to read and write files'),
+            'codec',
+        )
+        self.add_main_option(
+            'label',
+            ord('L'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.STRING,
+            _('Display <label> instead of the file name'),
+            'label',
+        )
+        self.add_main_option(
+            'modified',
+            ord('m'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Create a new tab for each modified file'),
+        )
+        self.add_main_option(
+            'revision',
+            ord('r'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.STRING,
+            _('File revision <rev>'),
+            'rev',
+        )
+        self.add_main_option(
+            'separate',
+            ord('s'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Create a new tab for each file'),
+        )
+        self.add_main_option(
+            'tab',
+            ord('t'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Start a new tab'),
+        )
+        self.add_main_option(
+            'vcs',
+            ord('V'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.STRING,
+            _('Version control system search order'),
+            'vcs-list',
+        )
+        self.add_main_option(
+            'line',
+            0,
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.STRING,
+            _('Start with line <line> selected'),
+            'line',
+        )
+        self.add_main_option(
+            'null-file',
+            0,
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Create a blank file comparison pane'),
+        )
+        self.add_main_option(
+            'ignore-space-change',
+            ord('b'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Ignore changes to white space'),
+        )
+        self.add_main_option(
+            'ignore-blank-lines',
+            ord('B'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Ignore changes in blank lines'),
+        )
+        self.add_main_option(
+            'ignore-end-of-line',
+            ord('E'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Ignore end of line differences'),
+        )
+        self.add_main_option(
+            'ignore-case',
+            ord('i'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Ignore case differences'),
+        )
+        self.add_main_option(
+            'ignore-all-space',
+            ord('w'),
+            GLib.OptionFlags.NONE,
+            GLib.OptionArg.NONE,
+            _('Ignore white space differences'),
+        )
+        self.set_option_context_summary(_(
+            '''Diffuse is a graphical tool for merging and comparing text files. Diffuse is
 able to compare an arbitrary number of files side-by-side and gives users the
 ability to manually adjust line matching and directly edit files. Diffuse can
-also retrieve revisions of files from several VCSs for comparison and merging.
+also retrieve revisions of files from several VCSs for comparison and merging.'''
+        ))
 
-Help Options:
-  ( -h | -? | --help )             Display this usage information
-  ( -v | --version )               Display version and copyright information
+    def do_activate(self):
+        self.window.present()
 
-Configuration Options:
-  --no-rcfile                      Do not read any resource files
-  --rcfile <file>                  Specify explicit resource file
+    def do_command_line(self, command_line):
+        options = command_line.get_options_dict()
+        # convert GVariantDict -> GVariant -> dict
+        options = options.end().unpack()
 
-General Options:
-  ( -c | --commit ) <rev>          File revisions <rev-1> and <rev>
-  ( -D | --close-if-same )         Close all tabs with no differences
-  ( -e | --encoding ) <codec>      Use <codec> to read and write files
-  ( -L | --label ) <label>         Display <label> instead of the file name
-  ( -m | --modified )              Create a new tab for each modified file
-  ( -r | --revision ) <rev>        File revision <rev>
-  ( -s | --separate )              Create a new tab for each file
-  ( -t | --tab )                   Start a new tab
-  ( -V | --vcs ) <vcs-list>        Version control system search order
-  --line <line>                    Start with line <line> selected
-  --null-file                      Create a blank file comparison pane
+        if 'version' in options:
+            print('%s %s\n%s' % (constants.APP_NAME, constants.VERSION, constants.COPYRIGHT))
+            return 0
 
-Display Options:
-  ( -b | --ignore-space-change )   Ignore changes to white space
-  ( -B | --ignore-blank-lines )    Ignore changes in blank lines
-  ( -E | --ignore-end-of-line )    Ignore end of line differences
-  ( -i | --ignore-case )           Ignore case differences
-  ( -w | --ignore-all-space )      Ignore white space differences'''))
-        return 0
-
-    # find the config directory and create it if it didn't exist
-    rc_dir = os.environ.get('XDG_CONFIG_HOME', None)
-    subdirs = ['diffuse']
-    if rc_dir is None:
-        rc_dir = os.path.expanduser('~')
-        subdirs.insert(0, '.config')
-    rc_dir = utils.make_subdirs(rc_dir, subdirs)
-
-    # find the local data directory and create it if it didn't exist
-    data_dir = os.environ.get('XDG_DATA_HOME', None)
-    subdirs = ['diffuse']
-    if data_dir is None:
-        data_dir = os.path.expanduser('~')
-        subdirs[:0] = ['.local', 'share']
-    data_dir = utils.make_subdirs(data_dir, subdirs)
-
-    # load resource files
-    i = 1
-    rc_files = []
-    if i < argc and args[i] == '--no-rcfile':
-        i += 1
-    elif i + 1 < argc and args[i] == '--rcfile':
-        i += 1
-        rc_files.append(args[i])
-        i += 1
-    else:
-        # parse system wide then personal initialization files
-        if utils.isWindows():
-            rc_file = os.path.join(utils.bin_dir, 'diffuserc')
-        else:
-            rc_file = os.path.join(utils.bin_dir, f'{sysconfigdir}/diffuserc')
-        for rc_file in rc_file, os.path.join(rc_dir, 'diffuserc'):
-            if os.path.isfile(rc_file):
-                rc_files.append(rc_file)
-    for rc_file in rc_files:
-        # convert to absolute path so the location of any processing errors are
-        # reported with normalized file names
-        rc_file = os.path.abspath(rc_file)
-        try:
-            theResources.parse(rc_file)
-        except IOError:
-            utils.logError(_('Error reading %s.') % (rc_file, ))
-
-    diff = Diffuse(rc_dir)
-
-    # load state
-    statepath = os.path.join(data_dir, 'state')
-    diff.loadState(statepath)
-
-    # process remaining command line arguments
-    encoding = None
-    revs = []
-    close_on_same = False
-    specs = []
-    had_specs = False
-    labels = []
-    funcs = {
-        'modified': diff.createModifiedFileTabs,
-        'commit': diff.createCommitFileTabs,
-        'separate': diff.createSeparateTabs,
-        'single': diff.createSingleTab
-    }
-    mode = 'single'
-    options = {}
-    while i < argc:
-        arg = args[i]
-        if len(arg) > 0 and arg[0] == '-':
-            if i + 1 < argc and arg in ['-c', '--commit']:
-                # specified revision
-                funcs[mode](specs, labels, options)
-                i += 1
-                specs, labels, options = [], [], {'commit': args[i]}
-                mode = 'commit'
-            elif arg in ['-D', '--close-if-same']:
-                close_on_same = True
-            elif i + 1 < argc and arg in ['-e', '--encoding']:
-                i += 1
-                encoding = args[i]
-                encoding = encodings.aliases.aliases.get(encoding, encoding)
-            elif arg in ['-m', '--modified']:
-                funcs[mode](specs, labels, options)
-                specs, labels, options = [], [], {}
-                mode = 'modified'
-            elif i + 1 < argc and arg in ['-r', '--revision']:
-                # specified revision
-                i += 1
-                revs.append((args[i], encoding))
-            elif arg in ['-s', '--separate']:
-                funcs[mode](specs, labels, options)
-                specs, labels, options = [], [], {}
-                # open items in separate tabs
-                mode = 'separate'
-            elif arg in ['-t', '--tab']:
-                funcs[mode](specs, labels, options)
-                specs, labels, options = [], [], {}
-                # start a new tab
-                mode = 'single'
-            elif i + 1 < argc and arg in ['-V', '--vcs']:
-                i += 1
-                diff.prefs.setString('vcs_search_order', args[i])
-                diff.preferences_updated()
-            elif arg in ['-b', '--ignore-space-change']:
-                diff.prefs.setBool('display_ignore_whitespace_changes', True)
-                diff.prefs.setBool('align_ignore_whitespace_changes', True)
-                diff.preferences_updated()
-            elif arg in ['-B', '--ignore-blank-lines']:
-                diff.prefs.setBool('display_ignore_blanklines', True)
-                diff.prefs.setBool('align_ignore_blanklines', True)
-                diff.preferences_updated()
-            elif arg in ['-E', '--ignore-end-of-line']:
-                diff.prefs.setBool('display_ignore_endofline', True)
-                diff.prefs.setBool('align_ignore_endofline', True)
-                diff.preferences_updated()
-            elif arg in ['-i', '--ignore-case']:
-                diff.prefs.setBool('display_ignore_case', True)
-                diff.prefs.setBool('align_ignore_case', True)
-                diff.preferences_updated()
-            elif arg in ['-w', '--ignore-all-space']:
-                diff.prefs.setBool('display_ignore_whitespace', True)
-                diff.prefs.setBool('align_ignore_whitespace', True)
-                diff.preferences_updated()
-            elif i + 1 < argc and arg == '-L':
-                i += 1
-                labels.append(args[i])
-            elif i + 1 < argc and arg == '--line':
-                i += 1
-                try:
-                    options['line'] = int(args[i])
-                except ValueError:
-                    utils.logError(_('Error parsing line number.'))
-            elif arg == '--null-file':
-                # add a blank file pane
-                if mode == 'single' or mode == 'separate':
-                    if len(revs) == 0:
-                        revs.append((None, encoding))
-                    specs.append((None, revs))
-                    revs = []
-                had_specs = True
+        # find the config directory and create it if it didn't exist
+        rc_dir = os.environ.get('XDG_CONFIG_HOME', None)
+        subdirs = ['diffuse']
+        if rc_dir is None:
+            rc_dir = os.path.expanduser('~')
+            subdirs.insert(0, '.config')
+        rc_dir = utils.make_subdirs(rc_dir, subdirs)
+        # find the local data directory and create it if it didn't exist
+        data_dir = os.environ.get('XDG_DATA_HOME', None)
+        subdirs = ['diffuse']
+        if data_dir is None:
+            data_dir = os.path.expanduser('~')
+            subdirs[:0] = ['.local', 'share']
+        data_dir = utils.make_subdirs(data_dir, subdirs)
+        # load resource files
+        rc_files = []
+        if 'no-rcfile' not in options:
+            # parse system wide then personal initialization files
+            if utils.isWindows():
+                rc_file = os.path.join(utils.bin_dir, 'diffuserc')
             else:
-                utils.logError(_('Skipping unknown argument "%s".') % (args[i], ))
-        else:
-            filename = diff.prefs.convertToNativePath(args[i])
+                rc_file = os.path.join(utils.bin_dir, self.sysconfigdir, 'diffuserc')
+            for rc_file in rc_file, os.path.join(rc_dir, 'diffuserc'):
+                if os.path.isfile(rc_file):
+                    rc_files.append(rc_file)
+        if 'rcfile' in options:
+            rc_files.append(options['rcfile'])
+        for rc_file in rc_files:
+            # convert to absolute path so the location of any processing errors are
+            # reported with normalized file names
+            rc_file = os.path.abspath(rc_file)
+            try:
+                theResources.parse(rc_file)
+            except IOError:
+                utils.logError(_('Error reading %s.') % (rc_file,))
+        self.window = diff = Diffuse(rc_dir, application=self)
+        # load state
+        self.statepath = os.path.join(data_dir, 'state')
+        self.window.loadState(self.statepath)
+        # process remaining command line arguments
+        encoding = None
+        revs = []
+        close_on_same = False
+        specs = []
+        had_specs = False
+        labels = []
+        funcs = {
+            'modified': diff.createModifiedFileTabs,
+            'commit': diff.createCommitFileTabs,
+            'separate': diff.createSeparateTabs,
+            'single': diff.createSingleTab,
+        }
+        mode = 'single'
+        opts = {}
+        if 'commit' in options:
+            # specified revision
+            funcs[mode](specs, labels, options)
+            specs, labels, opts = [], [], {'commit': options['commit']}
+            mode = 'commit'
+        if 'close-if-same' in options:
+            close_on_same = True
+        if 'encoding' in options:
+            encoding = options['encoding']
+            encoding = encodings.aliases.aliases.get(encoding, encoding)
+        if 'modified' in options:
+            funcs[mode](specs, labels, opts)
+            specs, labels, opts = [], [], {}
+            mode = 'modified'
+        if 'revision' in options:
+            # specified revision
+            revs.append((options['revision'], encoding))
+        if 'separate' in options:
+            funcs[mode](specs, labels, opts)
+            specs, labels, opts = [], [], {}
+            # open items in separate tabs
+            mode = 'separate'
+        if 'tab' in options:
+            funcs[mode](specs, labels, opts)
+            specs, labels, opts = [], [], {}
+            # start a new tab
+            mode = 'single'
+        if 'vcs' in options:
+            diff.prefs.setString('vcs_search_order', options['vcs'])
+            diff.preferences_updated()
+        if 'ignore-space-change' in options:
+            diff.prefs.setBool('display_ignore_whitespace_changes', True)
+            diff.prefs.setBool('align_ignore_whitespace_changes', True)
+            diff.preferences_updated()
+        if 'ignore-blank-lines' in options:
+            diff.prefs.setBool('display_ignore_blanklines', True)
+            diff.prefs.setBool('align_ignore_blanklines', True)
+            diff.preferences_updated()
+        if 'ignore-end-of-line' in options:
+            diff.prefs.setBool('display_ignore_endofline', True)
+            diff.prefs.setBool('align_ignore_endofline', True)
+            diff.preferences_updated()
+        if 'ignore-case' in options:
+            diff.prefs.setBool('display_ignore_case', True)
+            diff.prefs.setBool('align_ignore_case', True)
+            diff.preferences_updated()
+        if 'ignore-all-space' in options:
+            diff.prefs.setBool('display_ignore_whitespace', True)
+            diff.prefs.setBool('align_ignore_whitespace', True)
+            diff.preferences_updated()
+        if 'label' in options:
+            labels.append(options['label'])
+        if 'line' in options:
+            try:
+                opts['line'] = int(options['line'])
+            except ValueError:
+                utils.logError(_('Error parsing line number.'))
+        if 'null-file' in options:
+            # add a blank file pane
+            if mode == 'single' or mode == 'separate':
+                if len(revs) == 0:
+                    revs.append((None, encoding))
+                specs.append((None, revs))
+                revs = []
+            had_specs = True
+        for arg in command_line.get_arguments()[1:]:
+            filename = diff.prefs.convertToNativePath(arg)
             if (mode == 'single' or mode == 'separate') and os.path.isdir(filename):
                 if len(specs) > 0:
                     filename = os.path.join(filename, os.path.basename(specs[-1][0]))
                 else:
-                    utils.logError(_(
-                        'Error processing argument "%s".  Directory not expected.') % (args[i], )
-                    )
+                    utils.logError(
+                        _('Error processing argument "%s".  Directory not expected.') % (arg,))
                     filename = None
             if filename is not None:
                 if len(revs) == 0:
@@ -1997,26 +2117,27 @@ Display Options:
                 specs.append((filename, revs))
                 revs = []
             had_specs = True
-        i += 1
-    if mode in ['modified', 'commit'] and len(specs) == 0:
-        specs.append((os.curdir, [(None, encoding)]))
-        had_specs = True
-    funcs[mode](specs, labels, options)
+        if mode in ['modified', 'commit'] and len(specs) == 0:
+            specs.append((os.curdir, [(None, encoding)]))
+            had_specs = True
+        funcs[mode](specs, labels, opts)
+        # create a file diff viewer if the command line arguments haven't
+        # implicitly created any
+        if not had_specs:
+            diff.newLoadedFileDiffViewer([])
+        elif close_on_same:
+            diff.closeOnSame()
+        nb = diff.notebook
+        n = nb.get_n_pages()
+        if n > 0:
+            nb.set_show_tabs(diff.prefs.getBool('tabs_always_show') or n > 1)
+            nb.get_nth_page(0).grab_focus()
+        self.activate()
+        return 0
 
-    # create a file diff viewer if the command line arguments haven't
-    # implicitly created any
-    if not had_specs:
-        diff.newLoadedFileDiffViewer([])
-    elif close_on_same:
-        diff.closeOnSame()
-    nb = diff.notebook
-    n = nb.get_n_pages()
-    if n > 0:
-        nb.set_show_tabs(diff.prefs.getBool('tabs_always_show') or n > 1)
-        nb.get_nth_page(0).grab_focus()
-        diff.show()
-        Gtk.main()
-        # save state
-        diff.saveState(statepath)
 
-    return 0
+def main(version, sysconfigdir):
+    constants.VERSION = version
+
+    app = Application(sysconfigdir)
+    return app.run(sys.argv)
diff --git a/src/diffuse/widgets.py b/src/diffuse/widgets.py
index df57872..21e0ebb 100644
--- a/src/diffuse/widgets.py
+++ b/src/diffuse/widgets.py
@@ -1853,23 +1853,44 @@ class FileDiffViewerBase(Gtk.Grid):
             can_select = self.mode in (EditMode.LINE, EditMode.CHAR) and f == self.current_pane
             can_swap = (f != self.current_pane)
 
-            menu = createMenu([
-                [_('Align with Selection'), self.align_with_selection_cb, [f, i], Gtk.STOCK_EXECUTE, None, can_align],  # noqa: E501
-                [_('Isolate'), self.button_cb, 'isolate', None, None, can_isolate],
-                [_('Merge Selection'), self.merge_lines_cb, f, None, None, can_merge],
+            menu = self._create_menu([
+                [_('Align with Selection'), self.align_with_selection_cb, [f, i], Gtk.STOCK_EXECUTE, can_align],  # noqa: E501
+                [_('Isolate'), self.button_cb, 'isolate', None, can_isolate],
+                [_('Merge Selection'), self.merge_lines_cb, f, None, can_merge],
                 [],
-                [_('Cut'), self.button_cb, 'cut', Gtk.STOCK_CUT, None, can_select],
-                [_('Copy'), self.button_cb, 'copy', Gtk.STOCK_COPY, None, can_select],
-                [_('Paste'), self.button_cb, 'paste', Gtk.STOCK_PASTE, None, can_select],
+                [_('Cut'), self.button_cb, 'cut', Gtk.STOCK_CUT, can_select],
+                [_('Copy'), self.button_cb, 'copy', Gtk.STOCK_COPY, can_select],
+                [_('Paste'), self.button_cb, 'paste', Gtk.STOCK_PASTE, can_select],
                 [],
-                [_('Select All'), self.button_cb, 'select_all', None, None, can_select],
-                [_('Clear Edits'), self.button_cb, 'clear_edits', Gtk.STOCK_CLEAR, None, can_isolate],  # noqa: E501
+                [_('Select All'), self.button_cb, 'select_all', None, can_select],
+                [_('Clear Edits'), self.button_cb, 'clear_edits', Gtk.STOCK_CLEAR, can_isolate],  # noqa: E501
                 [],
-                [_('Swap with Selected Pane'), self.swap_panes_cb, f, None, None, can_swap]
+                [_('Swap with Selected Pane'), self.swap_panes_cb, f, None, can_swap]
             ])
             menu.attach_to_widget(self)
             menu.popup(None, None, None, None, event.button, event.time)
 
+    @staticmethod
+    def _create_menu(specs):
+        menu = Gtk.Menu()
+        for spec in specs:
+            if len(spec) > 0:
+                (label, cb, cb_data, image_stock_name, sensitive) = spec
+                item = Gtk.ImageMenuItem.new_with_mnemonic(label)
+                item.set_use_underline(True)
+                item.set_sensitive(sensitive)
+                if image_stock_name is not None:
+                    image = Gtk.Image()
+                    image.set_from_stock(image_stock_name, Gtk.IconSize.MENU)
+                    item.set_image(image)
+                if cb is not None:
+                    item.connect('activate', cb, cb_data)
+            else:
+                item = Gtk.SeparatorMenuItem()
+            item.show()
+            menu.append(item)
+        return menu
+
     # callback used to notify us about click and drag motion
     def darea_motion_notify_cb(self, widget, event, f):
         if event.state & Gdk.ModifierType.BUTTON1_MASK:
@@ -3708,51 +3729,6 @@ class FileDiffViewerBase(Gtk.Grid):
         self._mergeBoth(True)
 
 
-# convenience method for creating a menu according to a template
-def createMenu(specs, radio=None, accel_group=None):
-    menu = Gtk.Menu()
-    for spec in specs:
-        if len(spec) > 0:
-            if len(spec) > 7 and spec[7] is not None:
-                g, k = spec[7]
-                if g not in radio:
-                    item = Gtk.RadioMenuItem.new_with_mnemonic_from_widget(None, spec[0])
-                    radio[g] = (item, {})
-                else:
-                    item = Gtk.RadioMenuItem.new_with_mnemonic_from_widget(radio[g][0], spec[0])
-                radio[g][1][k] = item
-            else:
-                item = Gtk.ImageMenuItem.new_with_mnemonic(spec[0])
-            cb = spec[1]
-            if cb is not None:
-                data = spec[2]
-                item.connect('activate', cb, data)
-            if len(spec) > 3 and spec[3] is not None:
-                image = Gtk.Image()
-                image.set_from_stock(spec[3], Gtk.IconSize.MENU)
-                item.set_image(image)
-            if accel_group is not None and len(spec) > 4:
-                a = theResources.getKeyBindings('menu', spec[4])
-                if len(a) > 0:
-                    key, modifier = a[0]
-                    item.add_accelerator(
-                        'activate',
-                        accel_group,
-                        key,
-                        modifier,
-                        Gtk.AccelFlags.VISIBLE)
-            if len(spec) > 5:
-                item.set_sensitive(spec[5])
-            if len(spec) > 6 and spec[6] is not None:
-                item.set_submenu(createMenu(spec[6], radio, accel_group))
-            item.set_use_underline(True)
-        else:
-            item = Gtk.SeparatorMenuItem()
-        item.show()
-        menu.append(item)
-    return menu
-
-
 class CharacterClass(IntFlag):
     ALPHANUMERIC = 0
     WHITESPACE = 1