Issue 4527 - Don't access potentially dead object in child/elemHide.js

lib/child/elemHide.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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 351 matching lines @@
           catch (e)
           {
             // Ignore NS_ERROR_ILLEGAL_VALUE - it will be thrown if we try to add
             // the stylesheet multiple times to the same document (the observer
             // will be notified twice for some documents).
             if (e.result != Cr.NS_ERROR_ILLEGAL_VALUE)
               throw e;
           }
         }
 
-        let host = subject.location.hostname;
+        let host = window.location.hostname;
         if (host)
         {
           try
           {
             let suffix = "=" + encodeURIComponent(host);
             if (specificOnly)
               suffix += "&specificonly";
             utils.loadSheetUsingURIString(this.styleURL.spec + suffix,
                 Ci.nsIStyleSheetService.USER_SHEET);
           }
@@ skipping 11 matching lines @@
       if (filter)
       {
         RequestNotifier.addNodeData(window.document, window.top, {
           contentType, docDomain, thirdParty, location, filter, filterType
         });
       }
     });
   }
 };
 observer.init();