--- a/testing/marionette/browser.js
+++ b/testing/marionette/browser.js
@@ -456,17 +456,17 @@ browser.Windows = class extends Map {
 
 // TODO(ato): Move this to testing/marionette/wm.js
 // after https://bugzil.la/1311041
 /**
  * Marionette representation of the {@link ChromeWindow} window state.
  *
  * @enum {string}
  */
-const WindowState = {
+this.WindowState = {
   Maximized: "maximized",
   Minimized: "minimized",
   Normal: "normal",
   Fullscreen: "fullscreen",
 
   /**
    * Converts {@link nsIDOMChromeWindow.windowState} to WindowState.
    *