Firefox is great in that regard: when you fill in a signup form it will automatically suggest you a long, generated password, and will then store it for you.
This is news for me. I've been using a local password manager for ages and disabled any browser form support since maybe the last century so I missed all those new functionalities. I'll keep using my password manager anyway, it's not only for the browser and not only for one device. I sync the db across devices with Syncthing, I don't login into any browser cloud sync.
That is not really unique to Firefox, right? Safari does it as well and I am pretty sure Chrome does it too (I am not a Chrome user, so I can't check).