Hi The previously used Sync service that used a Sync key was replaced in September 30, 2015 with the current Sync version that uses a Firefox Account with an email address and password. So if you have a Sync key from that old Sync version then this is of no use and you will have to create a new Sync account. *https://support.mozilla.org/de/kb/sync-your-firefox-bookmarks-history-passwords-and- If you are already using the new Sync version and you have generated a recovery key then see this article. *https://support.mozilla.org/de/kb/reset-your-firefox-account-password-recovery-keys Note that data stored on the Sync server doesn't last forever and you may only have bookmarks and logins.