--- a/browser/base/content/browser-sets.inc
+++ b/browser/base/content/browser-sets.inc
@@ -280,16 +280,19 @@
     <key id="key_fullScreen" key="&fullScreenCmd.macCommandKey;" command="View:FullScreen" modifiers="accel,control"/>
     <key id="key_fullScreen_old" key="&fullScreenCmd.macCommandKey;" command="View:FullScreen" modifiers="accel,shift"/>
     <key keycode="VK_F11" command="View:FullScreen"/>
 #endif
     <key id="key_toggleReaderMode" key="&toggleReaderMode.key;" command="View:ReaderView" modifiers="accel,alt" disabled="true"/>
     <key key="&reloadCmd.commandkey;" command="Browser:Reload" modifiers="accel" id="key_reload"/>
     <key key="&reloadCmd.commandkey;" command="Browser:ReloadSkipCache" modifiers="accel,shift"/>
     <key id="key_viewSource" key="&pageSourceCmd.commandkey;" command="View:PageSource" modifiers="accel"/>
+#ifdef XP_MACOSX
+    <key id="key_viewSourceSafari" key="&pageSourceCmd.SafariCommandKey;" command="View:PageSource" modifiers="accel,alt"/>
+#endif
 #ifndef XP_WIN
     <key id="key_viewInfo"   key="&pageInfoCmd.commandkey;"   command="View:PageInfo"   modifiers="accel"/>
 #endif
     <key id="key_find" key="&findOnCmd.commandkey;" command="cmd_find" modifiers="accel"/>
     <key id="key_findAgain" key="&findAgainCmd.commandkey;" command="cmd_findAgain" modifiers="accel"/>
     <key id="key_findPrevious" key="&findAgainCmd.commandkey;" command="cmd_findPrevious" modifiers="accel,shift"/>
 #ifdef XP_MACOSX
     <key id="key_findSelection" key="&findSelectionCmd.commandkey;" command="cmd_findSelection" modifiers="accel"/>

--- a/browser/locales/en-US/chrome/browser/browser.dtd
+++ b/browser/locales/en-US/chrome/browser/browser.dtd
@@ -95,16 +95,23 @@ when there are no windows but Firefox is
 <!ENTITY toolbarContextMenu.bookmarkAllTabs.label "Bookmark All Tabs…">
 <!ENTITY toolbarContextMenu.bookmarkAllTabs.accesskey "T">
 <!ENTITY toolbarContextMenu.undoCloseTab.label "Undo Close Tab">
 <!ENTITY toolbarContextMenu.undoCloseTab.accesskey "U">
 
 <!ENTITY pageSourceCmd.label "Page Source">
 <!ENTITY pageSourceCmd.accesskey "o">
 <!ENTITY pageSourceCmd.commandkey "u">
+<!-- LOCALIZATION NOTE (pageSourceCmd.SafariCommandKey should match the
+Option+Command keyboard shortcut letter that Safari and Chrome use for "View
+Source" on macOS. pageSourceCmd.commandkey above is Firefox's official keyboard
+shortcut shown in the GUI. SafariCommandKey is an alias provided for the
+convenience of Safari and Chrome users on macOS. See bug 1398988. -->
+<!ENTITY pageSourceCmd.SafariCommandKey "u">
+
 <!ENTITY pageInfoCmd.label "Page Info">
 <!ENTITY pageInfoCmd.accesskey "I">
 <!ENTITY pageInfoCmd.commandkey "i">
 <!ENTITY mirrorTabCmd.label "Mirror Tab">
 <!ENTITY mirrorTabCmd.accesskey "m">
 <!-- LOCALIZATION NOTE (enterFullScreenCmd.label, exitFullScreenCmd.label):
 These should match what Safari and other Apple applications use on OS X Lion. -->
 <!ENTITY enterFullScreenCmd.label "Enter Full Screen">