just adding that granted FF already has a decent password manager there are also reliable, free and open source and audited independent password manager like as
- Bitwarden (remote service as basic or premium plan, optionally self hosted, user friendly service, very likely has some account migration wizard tool to help importing data from browsers) and
- KeepassXC (local, user managed, a bit techy)
which both can plug in any browser through their respective extension.
Being both an independent option from the browser they help the user not making him vendor locked to his browser through his saved data.