Apple now has a dedicated iCloud Passwords add-on designed for the Firefox browser, which means Firefox users can access passwords and logins stored in the Passwords app or iCloud Keychain when using Firefox on a Mac.
The extension is being distributed by Apple, but it appears that it was originally created by a third-party developer and later taken over and updated by Apple.
With the iCloud Passwords extension, passwords stored in iCloud Keychain can be securely filled in automatically when signing into websites in Firefox. New passwords created in Firefox are also saved to iCloud Keychain, which makes them available across Apple devices, plus there is an option to generate verification codes.
Read more at MacRumors.com