Issue 3407 - Don`t access content window when closing blockable items

lib/ui.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2015 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 1737 matching lines @@
     else
     {
       let {addBottomBar, removeBottomBar, getBrowser} = require("appSupport");
       let mustDetach = !addBottomBar || !removeBottomBar || !("abp-bottombar-container" in this.overlay);
       let detach = mustDetach || Prefs.detachsidebar;
       if (!detach && window.document.getElementById("abp-bottombar"))
       {
         removeBottomBar(window);
 
         let browser = (getBrowser ? getBrowser(window) : null);
+        if (browser && "selectedBrowser" in browser)
+          browser = browser.selectedBrowser;
         if (browser)
-          browser.contentWindow.focus();
+          browser.focus();
       }
       else if (!detach)
       {
         addBottomBar(window, this.overlay["abp-bottombar-container"]);
         let element = window.document.getElementById("abp-bottombar");
         if (element)
         {
           element.setAttribute("width", Prefs.blockableItemsSize.width);
           element.setAttribute("height", Prefs.blockableItemsSize.height);
 
@@ skipping 126 matching lines @@
   ["abp-command-contribute-hide", "command", UI.hideContributeButton.bind(UI)],
   ["abp-command-toggleshownotifications", "command", Notification.toggleIgnoreCategory.bind(Notification, "*", null)]
 ];
 
 onShutdown.add(function()
 {
   for (let window of UI.applicationWindows)
     if (UI.isBottombarOpen(window))
       UI.toggleBottombar(window);
 });