bitwarden, which i use every day, integrates with firefox and can generate passwords for you pretty easily, but probably not as directly as firefox will. but it can integrate with apps so you dont have to open firefox to retrieve your passwords. bitwarden has stronger encryption but firefox is probably fine for general use.

historically there has been some security issues https://www.bleepingcomputer.com/news/security/firefox-master-password-system-has-been-poorly-secured-for-the-past-9-years/ but it seems like the consensus today is that FF password manager is fine as long as you have a good master password and two-factor authentication on your account.

you can read a little more here https://www.reddit.com/r/firefox/comments/1eaiev9/firefox_password_versus_password_managers/