Bug 1680069 - proton root attribute and pref work, r=jaws,mconley

Differential Revision: https://phabricator.services.mozilla.com/D98375

browser/app/profile/firefox.js

@@ -825,6 +825,8 @@ pref("browser.preferences.defaultPerformanceSettings.enabled", true);
 
 pref("browser.preferences.exposeHTTPSOnly", true);
 
+pref("browser.proton.enabled", false);
+
 pref("browser.download.show_plugins_in_list", true);
 pref("browser.download.hide_plugins_without_extensions", true);
 

browser/base/content/browser.js

@@ -552,6 +552,16 @@ XPCOMUtils.defineLazyPreferenceGetter(
   false
 );
 
+XPCOMUtils.defineLazyPreferenceGetter(
+  this,
+  "gProton",
+  "browser.proton.enabled",
+  false,
+  (pref, oldValue, newValue) => {
+    document.documentElement.toggleAttribute("proton", newValue);
+  }
+);
+
 customElements.setElementCreationCallback("translation-notification", () => {
   Services.scriptloader.loadSubScript(
     "chrome://browser/content/translation-notification.js",
@@ -1698,6 +1708,8 @@ 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();