--- a/browser/base/content/browser-sets.inc
+++ b/browser/base/content/browser-sets.inc
@@ -360,19 +360,17 @@
 # On OS X, dark voodoo magic invokes the quit code for this key.
 # So we're not adding the attribute on OSX because of backwards/add-on compat.
 # See bug 1369909 for background on this.
 #ifndef XP_MACOSX
          command="cmd_quitApplication"
 #endif
          reserved="true"/>
 
-#ifdef FULL_BROWSER_WINDOW
     <key id="key_undoCloseTab" command="History:UndoCloseTab" key="&tabCmd.commandkey;" modifiers="accel,shift"/>
-#endif
     <key id="key_undoCloseWindow" command="History:UndoCloseWindow" key="&newNavigatorCmd.key;" modifiers="accel,shift"/>
 
 #ifdef XP_GNOME
 #define NUM_SELECT_TAB_MODIFIER alt
 #else
 #define NUM_SELECT_TAB_MODIFIER accel
 #endif
 

--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -1951,17 +1951,17 @@ if (AppConstants.platform == "macosx") {
   // macWindow.inc.xul
   gBrowserInit.nonBrowserWindowStartup = function() {
     // Disable inappropriate commands / submenus
     var disabledItems = ["Browser:SavePage",
                          "Browser:SendLink", "cmd_pageSetup", "cmd_print", "cmd_find", "cmd_findAgain",
                          "viewToolbarsMenu", "viewSidebarMenuMenu", "Browser:Reload",
                          "viewFullZoomMenu", "pageStyleMenu", "charsetMenu", "View:PageSource", "View:FullScreen",
                          "viewHistorySidebar", "Browser:AddBookmarkAs", "Browser:BookmarkAllTabs",
-                         "View:PageInfo"];
+                         "View:PageInfo", "History:UndoCloseTab"];
     var element;
 
     for (let disabledItem of disabledItems) {
       element = document.getElementById(disabledItem);
       if (element)
         element.setAttribute("disabled", "true");
     }
 

--- a/browser/base/content/browser.xul
+++ b/browser/base/content/browser.xul
@@ -84,19 +84,17 @@
   XPCOMUtils.defineLazyScriptGetter(window,
     ["PlacesInsertionPoint", "PlacesController", "PlacesControllerDragHelper"],
      "chrome://browser/content/places/controller.js");
 </script>
 
 # All sets except for popupsets (commands, keys, stringbundles and broadcasters)
 # *must* go into the browser-sets.inc file so that they can be shared with other
 # top level windows in macWindow.inc.xul.
-#define FULL_BROWSER_WINDOW
 #include browser-sets.inc
-#undef FULL_BROWSER_WINDOW
 
   <popupset id="mainPopupSet">
     <menupopup id="tabContextMenu"
                onpopupshowing="if (event.target == this) TabContextMenu.updateContextMenu(this);"
                onpopuphidden="if (event.target == this) TabContextMenu.contextTab = null;">
       <menuitem id="context_reloadTab" label="&reloadTab.label;" accesskey="&reloadTab.accesskey;"
                 oncommand="gBrowser.reloadTab(TabContextMenu.contextTab);"/>
       <menuitem id="context_toggleMuteTab" oncommand="TabContextMenu.contextTab.toggleMuteAudio();"/>