I found the answer :). It wasn't obvious to find in the FAQ tho.
"In future versions of Firefox, this feature will be built in and will work with the Master Password feature. This addon is a preview of what’s to come built into Firefox!" -- https://lockwise.firefox.com/faq.html
I think the marketing team should have promoted a bit more the fact that it is going to replace the current implementation but like you I'm really glad they're going for a more modular approach
I think Firefox is trying to do something similar with Firefox accounts and with their Firefox Send, Firefox Monitor and Firefox Lockwise services.
Firefox Lockwise is actually a pretty cool password manager. Having it automatically generate and save a password for you when you sign up somewhere is really a seamless experience.
Ook Firefox (Lockwise) waarschuwt verder hebben ze sinds kort FireFox Monitor ingebouwd in de browser waarmee je wordt gewaarschuwd of de website al eerder een data breach heeft gehad.
I assume it can be found in Mozilla website (here) and indeed the Github repo you've mentioned belonges to Mozilla.
But to answear your question, Lockwise seems to be secure and conveninet for storing and sharing your passwords across devices.
Its in the FAQ.
> > What security technologies does Firefox Lockwise use? > > Firefox Lockwise uses the following technologies to protect your data: > > * AES-256-GCM encryption, a tamper-resistant block cipher technology. > * onepw protocol to sign into Firefox Accounts and obtain encryption keys. > * PBKDF2 and HKDF with SHA-256 to create the encryption key from your Firefox Accounts username and password. > > All of this is done on your device, so Mozilla cannot know your password and cannot read your data.