fix: Fixed essential tabs appearing on private mode and updated tests, b=closes #8918, c=tabs, tests, glance, workspaces

src/zen/tests/workspaces/browser.toml

@@ -7,4 +7,6 @@ support-files = [
 ["browser_workspace_bookmarks.js"]
 ["browser_double_click_newtab.js"]
 ["browser_overflow_scrollbox.js"]
+
 ["browser_private_mode.js"]
+["browser_private_mode_startup.js"]

src/zen/tests/workspaces/browser_private_mode.js

@@ -3,7 +3,7 @@
 
 'use strict';
 
-add_task(async function testPrivateMode() {
+add_task(async function test_Private_Mode() {
   await SpecialPowers.pushPrefEnv({
     set: [['privacy.userContext.enabled', true]],
   });

src/zen/tests/workspaces/browser_private_mode_startup.js

@@ -0,0 +1,22 @@
+/* Any copyright is dedicated to the Public Domain.
+   https://creativecommons.org/publicdomain/zero/1.0/ */
+
+'use strict';
+
+add_task(async function test_Private_Mode_Startup() {
+  let privateWindow = await BrowserTestUtils.openNewBrowserWindow({
+    private: true,
+  });
+  await privateWindow.gZenWorkspaces.promiseInitialized;
+  await new Promise((resolve) => {
+    setTimeout(() => {
+      Assert.equal(
+        privateWindow.gBrowser.tabs.length,
+        1,
+        'Private window should start with one tab'
+      );
+      resolve();
+    }, 1000);
+  });
+  await BrowserTestUtils.closeWindow(privateWindow);
+});