If there was no sync set or other synced devices the chance to find or restore is won't happen. Firefox account isn't the same as the Browser saved login/password/bookmarks. Since you reinstalled anything that was on there is wiped clean. If this was install no sync backed or copy Firefox instructions backing up there nothing that can be done since this isn't Firefox caused.

Did you possibly reset the password of the Sync account because you forgot the password?

Resetting the password for the Firefox Account because you do not remember the password will remove all data stored on the Sync server because this password is used to encrypt your data before it is uploaded to the Sync server and only this password or a possible recovery key can decrypt this data.

You can install the About Sync extension in Firefox 72 and newer on desktop to check what data is stored on the Sync server via the about:sync page provided by this extension.

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

Close and restart Firefox to access the about:sync page added by this extension (see the about:about page for possible about pages).

Did you possibly reset the password of the Sync account because you forgot the password?

Yes I did ! I still have access to the C:/ drive that I backed up but I access it won´t help recover those passwords.