Issue 5094 - The MutationObserver callback was wrong

include.preload.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 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 111 matching lines @@
   {
     if (/^(?!https?:)[\w-]+:/i.test(urls[i]))
       urls.splice(i--, 1);
   }
 
   return urls;
 }
 
 function hideElement(element)
 {
-  function doHide(el)
+  function doHide()
   {
     let propertyName = "display";
     let propertyValue = "none";
-    if (el.localName == "frame")
+    if (element.localName == "frame")
     {
       propertyName = "visibility";
       propertyValue = "hidden";
     }
 
-    if (el.style.getPropertyValue(propertyName) != propertyValue ||
-        el.style.getPropertyPriority(propertyName) != "important")
-      el.style.setProperty(propertyName, propertyValue, "important");
+    if (element.style.getPropertyValue(propertyName) != propertyValue ||
+        element.style.getPropertyPriority(propertyName) != "important")
+      element.style.setProperty(propertyName, propertyValue, "important");
   }
 
-  doHide(element);
+  doHide();
 
   new MutationObserver(doHide).observe(
     element, {
       attributes: true,
       attributeFilter: ["style"]
     }
   );
 }
 
 function checkCollapse(element)
@@ skipping 333 matching lines @@
     checkCollapse(event.target);
   }, true);
 
   document.addEventListener("load", event =>
   {
     let element = event.target;
     if (/^i?frame$/.test(element.localName))
       checkCollapse(element);
   }, true);
 }