Resetting the password of the Firefox Account is not a good idea as that will reset all data stored on the Sync server, so I'm afraid that your data is lost. Note that Sync isn't designed to be used as a backup, but is merely meant to sync data between connected devices and best is always to backup your personal data locally. *https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles Aren't there any profiles left that you can use to recover this profile data ? *https://support.mozilla.org/en-US/kb/recover-user-data-missing-after-firefox-update