Starting with Firefox version 76, you may be be asked to log in with your Windows or Mac OS password or biometrics ID (Note: this is not your Firefox Account login) when you attempt to copy, edit or view your saved passwords. This is to protect you from attackers who might try to access your logins.
This feature is enabled in Firefox Nightly but is currently disabled in other Firefox versions, except for testing. Mozilla is planning to improve this feature and enable it in a future release.
For more information, see Secure Firefox passwords with device sign-in.