This is all I have on Sync :

• https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer
• https://support.mozilla.org/en-US/products/firefox/sync
• https://support.mozilla.org/en-US/kb/how-do-i-choose-what-types-information-sync-firefox
• https://support.mozilla.org/en-US/kb/firefox-sync-troubleshooting-and-tips
• https://support.mozilla.org/en-US/kb/change-primary-email-address-firefox-accounts

There is contact info in this and yes do have to create a account and wait : https://support.mozilla.org/en-US/kb/forum-response-firefox-sync-verification-email-faq

Please let us know if this solved your issue or if need further assistance.

Do you have any other devices connected to that Sync account? If so, is your Firefox data still present on those devices?

If not and only one device was connected to Sync - Sync was never intended to be used as a backup medium.

By far the biggest support issue that we see with Sync is with users trying to use Sync to back up a solitary device when they reformat their computer or reinstall their Windows operating system.

Unfortunately, when used in that manner if the user should reset their Sync password before they recover their data via the Sync their data is gone. The original password was used to encrypt their data and a new / different password is useless - it just can't decrypt that data thus rendering the data worthless. For maintenance purposes when the Firefox Account password is reset the worthless data is cleared from the Sync server to allow the user to continue using that Sync account, and not need to setup a new account using a different email address.

So if another device was connected to that same Sync account simply logging into Sync would "restore" the Firefox data to the Sync server and then that data could be sent to the reformatted device.