Firefox sync made the criminal sin of implementing end-to-end encryption, enabling it by default, and being insufficiently clear to people that their passwords are lost forever when they forget the master password.

This provides a really terrible UX to "normal" users. I woulnd't recommend that option to anybody who doesn't already know what E2E is and what tradeoffs it has.

Google's implementation is a lot better in that regard, at least they offer plenty of avenues for account recovery.