Bug 1778722 - Hide existing "Add-ons and themes" widget when "unifiedExtensions" pref is set. r=rpl

Note: the pref now requires a restart.

Depends on D151497

Differential Revision: https://phabricator.services.mozilla.com/D151699

browser/components/customizableui/CustomizableWidgets.jsm

@@ -296,6 +296,12 @@ const CustomizableWidgets = [
     id: "add-ons-button",
     shortcutId: "key_openAddons",
     l10nId: "toolbar-addons-themes-button",
+    onBeforeCreated() {
+      // If the pref is set to `true`, we won't create this widget.
+      return !Services.prefs.getBoolPref(
+        "extensions.unifiedExtensions.enabled"
+      );
+    },
     onCommand(aEvent) {
       let win = aEvent.target.ownerGlobal;
       win.BrowserOpenAddonsMgr();