diff --git a/browser/base/content/browser-menubar.inc b/browser/base/content/browser-menubar.inc
index 55834bad8d2..197a5894239 100644
--- a/browser/base/content/browser-menubar.inc
+++ b/browser/base/content/browser-menubar.inc
@@ -88,7 +88,9 @@
   
             <menu id="edit-menu" label="&editMenu.label;"
                   accesskey="&editMenu.accesskey;">
-              <menupopup id="menu_EditPopup">
+              <menupopup id="menu_EditPopup"
+                         onpopupshowing="updateEditUIVisibility()"
+                         onpopuphidden="updateEditUIVisibility()">
                 <menuitem label="&undoCmd.label;"
                           key="key_undo"
                           accesskey="&undoCmd.accesskey;"
diff --git a/browser/base/content/browser.js b/browser/base/content/browser.js
index 806d79a9c7a..75741ea8947 100644
--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -114,6 +114,10 @@ var gBookmarkAllTabsHandler = null;
 var gClickAndHoldTimer = null;
 #endif
 
+#ifndef XP_MACOSX
+var gEditUIVisible = true;
+#endif
+
 /**
 * We can avoid adding multiple load event listeners and save some time by adding
 * one listener that calls all real handlers.
@@ -1064,6 +1068,10 @@ function delayedStartup()
   // downloads will start right away, and getting the service again won't hurt.
   setTimeout(function() Cc["@mozilla.org/download-manager;1"].
                         getService(Ci.nsIDownloadManager), 10000);
+
+#ifndef XP_MACOSX
+  updateEditUIVisibility();
+#endif
 }
 
 function BrowserShutdown()
@@ -3087,6 +3095,10 @@ function BrowserToolboxCustomizeDone(aToolboxChanged)
     gHomeButton.updateTooltip();
     gIdentityHandler._cacheElements();
     window.XULBrowserWindow.init();
+
+#ifndef XP_MACOSX
+  updateEditUIVisibility();
+#endif
   }
 
   UpdateUrlbarSearchSplitterState();
@@ -3127,6 +3139,62 @@ function BrowserToolboxCustomizeDone(aToolboxChanged)
 #endif
 }
 
+/**
+ * Update the global flag that tracks whether or not any edit UI (the Edit menu,
+ * edit-related items in the context menu, and edit-related toolbar buttons
+ * is visible, then update the edit commands' enabled state accordingly.  We use
+ * this flag to skip updating the edit commands on focus or selection changes
+ * when no UI is visible to improve performance (including pageload performance,
+ * since focus changes when you load a new page).
+ *
+ * If the UI is visible, we use goUpdateEd
+ * If the UI isn't visible, we enable all edit commands so keyboard shortcuts
+ * still work and just lazily disable them as needed when the user presses a
+ * shortcut.
+ *
+ * This doesn't work on Mac, since Mac menus flash when users press their
+ * keyboard shortcuts, so edit UI is essentially always visible on the Mac,
+ * and we need to always update the edit commands.  Thus on Mac this function
+ * is a no op.
+ */
+function updateEditUIVisibility()
+{
+#ifndef XP_MACOSX
+  let editMenuPopupState = document.getElementById("menu_EditPopup").state;
+  let contextMenuPopupState = document.getElementById("contentAreaContextMenu").state;
+
+  // The UI is visible if the Edit menu is opening or open, if the context menu
+  // is open, or if the toolbar has been customized to include the Cut, Copy,
+  // or Paste toolbar buttons.
+  gEditUIVisible = editMenuPopupState == "showing" ||
+                   editMenuPopupState == "open" ||
+                   contextMenuPopupState == "showing" ||
+                   contextMenuPopupState == "open" ||
+                   document.getElementById("cut-button") ||
+                   document.getElementById("copy-button") ||
+                   document.getElementById("paste-button") ? true : false;
+
+  // If UI is visible, update the edit commands' enabled state to reflect
+  // whether or not they are actually enabled for the current focus/selection.
+  if (gEditUIVisible)
+    goUpdateGlobalEditMenuItems();
+
+  // Otherwise, enable all commands, so that keyboard shortcuts still work,
+  // then lazily determine their actual enabled state when the user presses
+  // a keyboard shortcut.
+  else {
+    goSetCommandEnabled("cmd_undo");
+    goSetCommandEnabled("cmd_redo");
+    goSetCommandEnabled("cmd_cut");
+    goSetCommandEnabled("cmd_copy");
+    goSetCommandEnabled("cmd_paste");
+    goSetCommandEnabled("cmd_selectAll");
+    goSetCommandEnabled("cmd_delete");
+    goSetCommandEnabled("cmd_switchTextDirection");
+  }
+#endif
+}
+
 var FullScreen =
 {
   toggle: function()
diff --git a/browser/base/content/browser.xul b/browser/base/content/browser.xul
index 3d7ef1ec99f..e3155edd873 100644
--- a/browser/base/content/browser.xul
+++ b/browser/base/content/browser.xul
@@ -138,8 +138,8 @@
     </popup>
 
     <popup id="contentAreaContextMenu"
-           onpopupshowing="if (event.target != this) return true; gContextMenu = new nsContextMenu(this, window.getBrowser()); return gContextMenu.shouldDisplay;"
-           onpopuphiding="if (event.target == this) { gContextMenu = null; }">
+           onpopupshowing="if (event.target != this) return true; updateEditUIVisibility(); gContextMenu = new nsContextMenu(this, window.getBrowser()); return gContextMenu.shouldDisplay;"
+           onpopuphiding="if (event.target == this) { gContextMenu = null; updateEditUIVisibility(); }">
 #include browser-context.inc
     </popup>
 
diff --git a/toolkit/content/editMenuOverlay.js b/toolkit/content/editMenuOverlay.js
index 20e9b644194..cd175cca31c 100644
--- a/toolkit/content/editMenuOverlay.js
+++ b/toolkit/content/editMenuOverlay.js
@@ -39,6 +39,14 @@
 // update menu items that rely on focus or on the current selection
 function goUpdateGlobalEditMenuItems()
 {
+  // Don't bother updating the edit commands if they aren't visible in any way
+  // (i.e. the Edit menu isn't open, nor is the context menu open, nor have the
+  // cut, copy, and paste buttons been added to the toolbars) for performance.
+  // This only works in applications/on platforms that set the gEditUIVisible
+  // flag, so we check to see if that flag is defined before using it.
+  if (typeof gEditUIVisible != "undefined" && !gEditUIVisible)
+    return;
+
   goUpdateCommand("cmd_undo");
   goUpdateCommand("cmd_redo");
   goUpdateCommand("cmd_cut");