Excellent extension! I have the family plan for Proton Pass only and after having tried some password managers, I think I have found my home. A great development is to now also have Proton Authenticator for one-time code generation, so that two-factor authentication actually stays two-factor (which it isn't if one-time password generation and passwords are handled by the same application with the same login procedures).
Great synchronisation with the Android app as well as in other browsers than Firefox, possibility to organise passwords, a shared vault in the family plan, and all end-to-end encrypted and independent from big tech - an essential extension.