Best is to stay with FEBE or manually create a backup of personal data in the Firefox profile folder.

Sync isn't designed to be used as a backup device, but merely to sync data between multiple devices. It is not guaranteed that you can restore data from the Sync server in case of problems with your OS or because you otherwise lost data. Requesting a new password because you forgot it or changing the password for the Firefox Sync account will wipe all data stored on the Sync server and you won't be able to retrieve data that was stored previously. Best is always to backup your personal data locally to be sure to be able to recover from issues.

timbrellow said

Do I need to use FEBE if my laptop dies and is replaced?

If the hard drive can be salvaged, it can be mounted on another computer.