Bug 1764090 - Fix browser_permissions_unsigned.js failure. r=thunderbird-reviewers,rjl

Bug 1754441 has some details. InstallTrigger will be removed at some point.

The test calls installTrigger(url), and obviously that would not work without InstallTrigger.

Differential Revision: https://phabricator.services.mozilla.com/D149518

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

mail/base/test/webextensions/browser_permissions_unsigned.js

@@ -6,6 +6,8 @@ const WARNING_ICON = "chrome://browser/skin/warning.svg";
 add_task(async function test_unsigned() {
   await SpecialPowers.pushPrefEnv({
     set: [
+      ["extensions.InstallTrigger.enabled", true],
+      ["extensions.InstallTriggerImpl.enabled", true],
       ["extensions.webapi.testing", true],
       ["extensions.install.requireBuiltInCerts", false],
       // Relax the user input requirements while running this test.