I would like to suggest that the password manager be protected by some kind of global password like the Master password, but rather than being input at the start of your session it would be input before accessing a password, or the manager itself. To make using passwords simpler but also more secure, a fingerprint or some other biometric could be required before the password autofills. This is a feature that came more recently to Google Chrome, and it is the first time that Chrome has a feature that would make me want to use it, because it is such a good idea. I would certianly trust Mozilla's implementation of it more than Google's, so I'm really hoping Mozilla adds a similar feature sometime soon.
Thank you