Bug 473444 - Help opens, but with a beep with cmd+? in prefwindow without overlayed/own key (this also makes us only open 1 help instance on mac from the prefwindow). r=gavin.

toolkit/content/widgets/preferences.xml

@@ -1117,7 +1117,14 @@
                keycode="&openHelp.commandkey;"
 #endif
                phase="capturing">
+      <![CDATA[
+        var helpButton = document.documentElement.getButton("help");
+        if (helpButton.disabled || helpButton.hidden)
+          return;
         this._fireEvent("dialoghelp", this);
+        event.stopPropagation();
+        event.preventDefault();
+      ]]>
       </handler>
     </handlers>
   </binding>