Bug 1660201 - Don't try to access node on domwindowclosed in ToolbarPanelHub.jsm r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D87758

browser/components/newtab/lib/ToolbarPanelHub.jsm

@@ -463,8 +463,11 @@ class _ToolbarPanelHub {
     );
   }
 
-  _hideAppmenuButton(win) {
-    this._hideElement(win.browser.ownerDocument, APPMENU_BUTTON_ID);
+  _hideAppmenuButton(win, windowClosed) {
+    // No need to do something if the window is going away
+    if (!windowClosed) {
+      this._hideElement(win.browser.ownerDocument, APPMENU_BUTTON_ID);
+    }
   }
 
   _showToolbarButton(win) {
@@ -484,7 +487,10 @@ class _ToolbarPanelHub {
   }
 
   _hideElement(document, id) {
-    document.getElementById(id).setAttribute("hidden", true);
+    const el = PanelMultiView.getViewNode(document, id);
+    if (el) {
+      el.setAttribute("hidden", true);
+    }
   }
 
   _sendTelemetry(ping) {

browser/components/newtab/test/unit/lib/ToolbarPanelHub.test.js

@@ -295,6 +295,17 @@ describe("ToolbarPanelHub", () => {
       instance._hideAppmenuButton(fakeWindow);
       assert.calledWith(fakeElementById.setAttribute, "hidden", true);
     });
+    it("should not do anything if the window is closed", () => {
+      instance._hideAppmenuButton(fakeWindow, true);
+      assert.notCalled(PanelMultiView.getViewNode);
+    });
+    it("should not throw if the element does not exist", () => {
+      let fn = instance._hideAppmenuButton.bind(null, {
+        browser: { ownerDocument: {} },
+      });
+      getViewNodeStub.returns(undefined);
+      assert.doesNotThrow(fn);
+    });
     it("should unhide toolbar button on _showToolbarButton()", async () => {
       await instance._showToolbarButton(fakeWindow);