Fixes 4328 - Multiple shadowRoot deprecated warnings

include.preload.js

Index: include.preload.js
diff --git a/include.preload.js b/include.preload.js
index 7acdbb149870180bd26785a5fd8a7432da1db692..f3b22dcf1496e26d84a7007627c3a46ab3b669cb 100644
--- a/include.preload.js
+++ b/include.preload.js
@@ -459,10 +459,15 @@ function init(document)
   //
   // Also, using shadow DOM causes issues on some Google websites,
   // including Google Docs, Gmail and Blogger (#1770, #2602, #2687).
+  //
+  // Finally since some users have both AdBlock and Adblock Plus installed we
+  // have to consider how the two extensions interact. For example we want to
+  // avoid creating the shadowRoot twice.
   if ("createShadowRoot" in document.documentElement &&
       !/\.(?:google|blogger)\.com$/.test(document.domain))
   {
-    shadow = document.documentElement.createShadowRoot();
+    shadow = document.documentElement.shadowRoot ||
+             document.documentElement.createShadowRoot();
     shadow.appendChild(document.createElement("shadow"));
 
     // Stop the website from messing with our shadowRoot
@@ -471,6 +476,8 @@ function init(document)
       runInDocument(document, function()
       {
         var ourShadowRoot = document.documentElement.shadowRoot;
+        if (!ourShadowRoot)
+          return;
         var desc = Object.getOwnPropertyDescriptor(Element.prototype, "shadowRoot");
         var shadowRoot = Function.prototype.call.bind(desc.get);