Issue 6441 - Avoid unnecessary shadow root

include.preload.js

Index: include.preload.js
===================================================================
--- a/include.preload.js
+++ b/include.preload.js
@@ -359,16 +359,24 @@
   {
     // Use Shadow DOM if available as to not mess with with web pages that
     // rely on the order of their own <style> tags (#309). However, creating
     // a shadow root breaks running CSS transitions. So we have to create
     // the shadow root before transistions might start (#452).
     if (!("createShadowRoot" in document.documentElement))
       return null;
 
+    // Use Shadow DOM only on Chrome version 65 and lower. Firefox's Shadow
+    // DOM v0 implementation is slightly different (e.g. no <shadow> element),
+    // while Chrome is deprecating Shadow DOM v0 in favor of Shadow DOM v1 and
+    // user style sheets.
+    let {application, applicationVersion} = require("info");
+    if (application != "chrome" || parseInt(applicationVersion) > 65)
+      return null;
+
     // Using shadow DOM causes issues on some Google websites,
     // including Google Docs, Gmail and Blogger (#1770, #2602, #2687).
     if (/\.(?:google|blogger)\.com$/.test(document.domain))
       return null;
 
     // 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.