Bug 1711519 - remove tabbrowser non-proton code and gProton global browser window property, r=jaws

Differential Revision: https://phabricator.services.mozilla.com/D116632

browser/base/content/browser.js

@@ -536,22 +536,6 @@ XPCOMUtils.defineLazyPreferenceGetter(
   false
 );
 
-/* Work around the pref callback being run after the document has been unlinked.
-   See bug 1543537. */
-var docWeak = Cu.getWeakReference(document);
-XPCOMUtils.defineLazyPreferenceGetter(
-  this,
-  "gProton",
-  "browser.proton.enabled",
-  false,
-  (pref, oldValue, newValue) => {
-    let doc = docWeak.get();
-    if (doc) {
-      doc.documentElement.toggleAttribute("proton", newValue);
-    }
-  }
-);
-
 /* Temporary pref while the dust settles around the updated tooltip design
    for tabs and bookmarks toolbar. This will eventually be removed and
    browser.proton.enabled will be used instead. */
@@ -1682,8 +1666,6 @@ var gBrowserInit = {
       document.documentElement.setAttribute("icon", "main-window");
     }
 
-    document.documentElement.toggleAttribute("proton", gProton);
-
     // Call this after we set attributes that might change toolbars' computed
     // text color.
     ToolbarIconColor.init();