Issue 673 - Check whether it is an HTML document before manipulating the DOM

include.preload.js

 /*
  * This file is part of Adblock Plus <http://adblockplus.org/>,
  * Copyright (C) 2006-2014 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 198 matching lines @@
       init(element.contentDocument);
 
       for (var tagName in typeMap)
         Array.prototype.forEach.call(element.contentDocument.getElementsByTagName(tagName), checkCollapse);
     }
   }, true);
 
   ext.backgroundPage.sendMessage({type: "get-selectors"}, setElemhideCSSRules);
 }
 
-if (document.documentElement instanceof HTMLElement)
+if (document instanceof HTMLDocument)
 {
   checkExceptionKey();
   init(document);
 }