Issue 4101 - Prevent runaway MutationObservers

include.preload.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 140 matching lines @@
       function collapseElement()
       {
         var propertyName = "display";
         var propertyValue = "none";
         if (element.localName == "frame")
         {
           propertyName = "visibility";
           propertyValue = "hidden";
         }
 
-        if (element.style.getPropertyValue(propertyName) !== propertyValue ||
-            element.style.getPropertyPriority(propertyName) !== "important")
+        if (element.style.getPropertyValue(propertyName) != propertyValue ||
+            element.style.getPropertyPriority(propertyName) != "important")
           element.style.setProperty(propertyName, propertyValue, "important");
       }
 
-      if (collapse && !element._collapsed)
+      if (collapse)
       {
         collapseElement();
-        element._collapsed = true;
 
         if (MutationObserver)
           new MutationObserver(collapseElement).observe(
             element, {
               attributes: true,
               attributeFilter: ["style"]
             }
           );
       }
     }
@@ skipping 435 matching lines @@
   }, true);
 
   return updateStylesheet;
 }
 
 if (document instanceof HTMLDocument)
 {
   checkSitekey();
   window.updateStylesheet = init(document);
 }