Did you create a backup of the sync key and other account information (name and password)?

Do you still have a Windows (desktop) installation or mobile device that has Sync installed and working?

• https://support.mozilla.org/kb/how-do-i-set-up-firefox-sync
• https://support.mozilla.org/kb/add-a-device-to-firefox-sync

• https://support.mozilla.org/kb/ive-lost-my-firefox-sync-account-information
• https://support.mozilla.org/kb/firefox-sync-troubleshooting-and-tips