I recommend going for a password manager. Bitwarden (and probably every other modern password manager) let's you import passwords from a file and Firefox let's you export all your passwords as a file. All you have to do is take your FF passwords and chuck them into your password manager of choice
Nah, Bitwarden is what I use. It has a free tier and a paid tier for $10/year that adds some extra features. You can read about both on their website.
You can also autofill on mobile and desktop with the mobile app and browser extension respectively (the mobile app also let's you autofill in any app that requires a login, which is nice)