diff --git a/browser/base/content/browser-init.js b/browser/base/content/browser-init.js
index f8d49ac2a3a62f389ea44b07a26fcb102abc0b24..c29415e10c776ebc435f33e55f8afb71f0dcf22a 100644
--- a/browser/base/content/browser-init.js
+++ b/browser/base/content/browser-init.js
@@ -237,6 +237,10 @@ var gBrowserInit = {
     gPrivateBrowsingUI.init();
     BrowserSearch.init();
     BrowserPageActions.init();
+
+    Services.scriptloader.loadSubScript("chrome://browser/content/ZenStartup.mjs", window);
+    Services.scriptloader.loadSubScript("chrome://browser/content/zenThemeModifier.js", window);
+
     if (gToolbarKeyNavEnabled) {
       ToolbarKeyboardNavigator.init();
     }