--- a/browser/base/content/test/webextensions/browser_permissions_optional.js
+++ b/browser/base/content/test/webextensions/browser_permissions_optional.js
@@ -27,17 +27,19 @@ add_task(async function test_request_per
       "optional_permissions": [
         "activeTab"
       ],
     },
   });
   await extension.startup();
 
   let url = await extension.awaitMessage("ready");
-  let win = window.open(url);
-  await extension.awaitMessage("pageReady");
+
+  await BrowserTestUtils.withNewTab({gBrowser, url}, async browser => {
+    await extension.awaitMessage("pageReady");
 
-  let winutils = SpecialPowers.getDOMWindowUtils(win);
-  winutils.sendKeyEvent("keypress", KeyEvent.DOM_VK_A, 0, 0);
-  await extension.awaitMessage("permsGranted");
+    await BrowserTestUtils.synthesizeKey("a", {}, browser);
+
+    await extension.awaitMessage("permsGranted");
+  });
 
   await extension.unload();
 });