Bug 1536473 - ext-menu onWindowOpen handler should wait for SidebarUI to be fully initialized. r=mixedpuppy,Gijs

Differential Revision: https://phabricator.services.mozilla.com/D24034

--HG--
extra : moz-landing-system : lando

browser/base/content/browser-sidebar.js

@@ -65,6 +65,12 @@ var SidebarUI = {
   _switcherArrow: null,
   _inited: false,
 
+  _initDeferred: PromiseUtils.defer(),
+
+  get promiseInitialized() {
+    return this._initDeferred.promise;
+  },
+
   get initialized() {
     return this._inited;
   },
@@ -83,6 +89,8 @@ var SidebarUI = {
     });
 
     this._inited = true;
+
+    this._initDeferred.resolve();
   },
 
   uninit() {

browser/components/extensions/parent/ext-menus.js

@@ -983,7 +983,7 @@ const menuTracker = {
     gMenuBuilder.build(subject);
   },
 
-  onWindowOpen(window) {
+  async onWindowOpen(window) {
     for (const id of menuTracker.menuIds) {
       const menu = window.document.getElementById(id);
       menu.addEventListener("popupshowing", menuTracker);
@@ -991,7 +991,10 @@ const menuTracker = {
 
     const sidebarHeader = window.document.getElementById("sidebar-switcher-target");
     sidebarHeader.addEventListener("SidebarShown", menuTracker.onSidebarShown);
-    if (window.SidebarUI.currentID === "viewBookmarksSidebar") {
+
+    await window.SidebarUI.promiseInitialized;
+
+    if (!window.closed && window.SidebarUI.currentID === "viewBookmarksSidebar") {
       menuTracker.onSidebarShown({currentTarget: sidebarHeader});
     }
   },