Hi It appears from your question that you are using Firefox Sync as a backup service. While it may be handy in some cases (such as [[Back up and transfer your Firefox data to a new device | transferring your data to a new device]]), we do not recommend relying on Sync for backup purposes. If you have a copy of your Firefox profile for desktop Firefox, you should be able to recover your bookmarks and other data. To restore bookmarks, see [[Restore bookmarks from backup or move them to another computer | this article]]. For instructions on recovering all of your data, see [[Restore bookmarks, passwords, and data from an old Firefox profile]]. If you have your data in Firefox on a mobile device, please follow [[How do I set up Sync on my computer?#w_connect-additional-devices-to-sync | these instructions]] to connect it to Sync and copy the data. Be aware! Resetting your Mozilla account password without a recovery key will erase your data from Mozilla servers. Make sure to [[Reset your Mozilla account password with Recovery Keys#w_generate-and-store-your-account-recovery-key | generate a recovery key]] in advance and safely store it. Hope this will help you resolve your issue!

I had the same problem when I reinstalled Firefox and had to manually enable sync for it to work. Click the profile icon in the top right (next to the address bar, not here) and check if there’s a message saying that sync is disabled. If so, just click on it and enable it. (You might have to log in again)