Firefox Beta and Developer Edition
Release Notes

Double-clicking on the Picture-in-Picture player window now puts it in fullscreen mode.

Warnings will now appear on saved logins if the same password was stored for a site which was subject to a website breach.

Improvements to password generation and saving to work with many sites which previously didn’t.

Accessing saved passwords in about:logins on Windows and macOS now requires the user to authenticate with their operating system if no master password is set.