Issue 2209 - Ignore scrolls offset when highlighting fixed positioned elements

include.postload.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 186 matching lines @@
   }
 
   return getURLsFromAttributes(element);
 }
 
 // Adds an overlay to an element, which is probably a Flash object
 function addElementOverlay(elt) {
   var zIndex = "auto";
   var position = "absolute";
 
+  var offsetX = window.scrollX;
+  var offsetY = window.scrollY;
+
   for (var e = elt; e; e = e.parentElement)
   {
     var style = getComputedStyle(e);
 
     // If the element isn't rendered (since its or one of its ancestor's
     // "display" property is "none"), the overlay wouldn't match the element.
     if (style.display == "none")
       return null;
 
     // If the element or one of its ancestors uses fixed postioning, the overlay
     // has to use fixed postioning too. Otherwise it might not match the element.
     if (style.position == "fixed")
+    {
       position = "fixed";
+      offsetX = offsetY = 0;
+    }
 
     // Determine the effective z-index, which is the highest z-index used
     // by the element and its offset ancestors, and increase it by one.
     // When using a lower z-index the element would cover the overlay.
     // When using a higher z-index the overlay might also cover other elements.
     if (style.position != "static" && style.zIndex != "auto")
     {
       var curZIndex = parseInt(style.zIndex, 10) + 1;
 
       if (zIndex == "auto" || curZIndex > zIndex)
         zIndex = curZIndex;
     }
   }
 
   var overlay = document.createElement('div');
   overlay.prisoner = elt;
   overlay.className = "__adblockplus__overlay";
   overlay.setAttribute('style', 'opacity:0.4; display:inline-box; overflow:hidden; box-sizing:border-box;');
   var rect = elt.getBoundingClientRect();
   overlay.style.width = rect.width + "px";
   overlay.style.height = rect.height + "px";
-  overlay.style.left = (rect.left + window.scrollX) + "px";
-  overlay.style.top = (rect.top + window.scrollY) + "px";
+  overlay.style.left = (rect.left + offsetX) + "px";
+  overlay.style.top = (rect.top + offsetY) + "px";
   overlay.style.position = position;
   overlay.style.zIndex = zIndex;
 
   // elt.parentNode.appendChild(overlay, elt);
   document.documentElement.appendChild(overlay);
   return overlay;
 }
 
 // Show dialog asking user whether she wants to add the proposed filters derived
 // from selected page element
@@ skipping 483 matching lines @@
           lastRightClickEventValid = false;
         else
           lastRightClickEvent = null;
         break;
     }
   });
 
   if (window == window.top)
     ext.backgroundPage.sendMessage({type: "report-html-page"});
 }