Was there sync setup or not? If you logged in with the new Firefox setup it will clear the sync server data if it didn't match with the data on local Firefox. Sync isn't a "BackupSystem" it syncs between devices only so if this is what you did then there is nothing anyone else can do at this point.

You can check what data is in the Sync cloud for your Mozilla Account using the About Sync add-on:

https://addons.mozilla.org/firefox/addon/about-sync/

After you install the add-on, you can type or paste about:sync in the address bar and press Enter to load it. The page shows each category of data currently found in the Sync cloud.

Anything useful under bookmarks?

If not, did you make any backups of the data on your computer before formatting?