I am not in favour of this. There are many exfilltration attacks on browser stored passwords. If the sync is e2ee it does not mean it is stored well. Also this sync will not be as cross platform as dedicated password managers.
https://support.mozilla.org/en-US/questions/1388181
As far as I know Firefox stores the passwords in plain text in the profile folder. You can set a master password, but I am unfamiliar where in keeps the decrypted keys during a session.