I think that I'd prefer Firefox allow Bitwarden and other password tools to replace Firefox's password implementation. That way you'd get the UI/UX of integrated password management, but the single-source-authoritative backend too.
(before someone points out that Bitwarden has an extension: I do know that, but I'd like to see more modular features in browsers rather than our-way-is-best)
And it had way better UX when auto-fill didn't work, because for some reason about:logins doesn't work on mobile, so you have to hunt through a menu mess to copy the password manually from Firefox.
I continued to use it (because they didn't stop it syncing) until I switched phone and so couldn't easily install it.
(before someone points out that Bitwarden has an extension: I do know that, but I'd like to see more modular features in browsers rather than our-way-is-best)