diff --git a/browser/components/extensions/ext-utils.js b/browser/components/extensions/ext-utils.js
index 17007d1baa81..fb3d749291dd 100644
--- a/browser/components/extensions/ext-utils.js
+++ b/browser/components/extensions/ext-utils.js
@@ -632,7 +632,7 @@ global.WindowManager = {
   convert(extension, window, getInfo) {
     let result = {
       id: this.getId(window),
-      focused: window == WindowManager.topWindow,
+      focused: window.document.hasFocus(),
       top: window.screenY,
       left: window.screenX,
       width: window.outerWidth,