Issue 5650 - Prevent attachShadowRoot to create closed shadow root.

inject.preload.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present 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 120 matching lines @@
         configurable: true, enumerable: true, get()
         {
           let thisShadow = shadowRoot(this);
           return thisShadow == ourShadowRoot ? null : thisShadow;
         }
       });
     }
   }
 
   /*
+   * Closed shadowRoot prevention.
+   * https://issues.adblockplus.org/ticket/5650
+   */
+  if ("attachShadow" in Element.prototype)
+  {
+    Element.prototype._attachShadow = Element.prototype.attachShadow;
+    Element.prototype.attachShadow = options => {
+      if (options && options.mode == "closed") {
+        options.mode = "open";
+      }
+      return this._attachShadow(options);
+    };
+  }
+
+  /*
    * Shared request checking code, used by both the WebSocket and
    * RTCPeerConnection wrappers.
    */
   let RealCustomEvent = window.CustomEvent;
 
   // If we've been injected into a frame via contentWindow then we can simply
   // grab the copy of checkRequest left for us by the parent document. Otherwise
   // we need to set it up now, along with the event handling functions.
   if (injectedIntoContentWindow)
     checkRequest = window[eventName];
@@ skipping 245 matching lines @@
   if (typeof sandbox != "string" || /(^|\s)allow-scripts(\s|$)/i.test(sandbox))
   {
     let script = document.createElement("script");
     script.type = "application/javascript";
     script.async = false;
     script.textContent = "(" + injected + ")('" + randomEventName + "');";
     document.documentElement.appendChild(script);
     document.documentElement.removeChild(script);
   }
 }