--- a/browser/components/customizableui/test/browser_989751_subviewbutton_class.js
+++ b/browser/components/customizableui/test/browser_989751_subviewbutton_class.js
@@ -10,16 +10,21 @@ var tempElement = null;
 function insertClassNameToMenuChildren(parentMenu) {
   let el = parentMenu.querySelector("menuitem:first-of-type");
   el.classList.add(kCustomClass);
   tempElement = el;
 }
 
 function checkSubviewButtonClass(menuId, buttonId, subviewId) {
   return async function() {
+    // Initialize DevTools before starting the test in order to create menuitems in
+    // menuWebDeveloperPopup.
+    Cu.import("resource://devtools/shared/Loader.jsm", {})
+        .require("devtools/client/framework/devtools-browser");
+
     info("Checking for items without the subviewbutton class in " + buttonId + " widget");
     let menu = document.getElementById(menuId);
     insertClassNameToMenuChildren(menu);
 
     let placement = CustomizableUI.getPlacementOfWidget(buttonId);
     let changedPlacement = false;
     if (!placement || placement.area != CustomizableUI.AREA_PANEL) {
       CustomizableUI.addWidgetToArea(buttonId, CustomizableUI.AREA_PANEL);