Quote:Firefox users who use a Firefox Account to sync data between devices and the cloud use a combination of a username and a password for authorization. Users may enable two-step authentication to improve security further.
The password is used to encrypt the data so that it is protected from any prying eyes. Even Mozilla, maker of Firefox and operator of the cloud storage where all the bits are stored, has no access to the data.
Considering that synced data may hold important and valuable information, such as account passwords, the browsing history or bookmarks, it is of utmost importance that only the owner of the data has access to it.
Firefox users who forgot the password up until now had no option to recover the data. While guessing might have worked for some to regain account access, most probably did not have luck using guesses.
Tip: you can check all Firefox Account connected devices and apps.

Full reading: https://www.ghacks.net/2018/09/27/how-to-create-firefox-account-recovery-keys/