Bug 1746577 - Restrict ensureExperimentToRolloutTransitionPerformed.js to Firefox. r=nalexander,Gijs,application-update-reviewers,bytesized

Differential Revision: https://phabricator.services.mozilla.com/D134125

toolkit/mozapps/update/tests/unit_aus_update/xpcshell.ini

@@ -46,5 +46,5 @@ reason = Update directory migration is currently Windows only
 [disableBackgroundUpdatesBackgroundTask.js]
 [disableBackgroundUpdatesNonBackgroundTask.js]
 [ensureExperimentToRolloutTransitionPerformed.js]
-run-if = os == 'win'
-reason = Feature is windows-specific.
+run-if = os == 'win' && appname == 'firefox'
+reason = Feature is Firefox-specific and Windows-specific.