While the service will eventually become free for everyone to use, it’s currently only available as a beta to Proton’s Lifetime and Visionary users for now.
As is the case with Proton’s other products, Proton Pass uses end-to-end encryption (E2EE) that’s supposed to keep your personal information away from prying eyes, including third parties and Proton itself. In addition to letting you store your usernames, passwords, and notes, you can also add any randomly generated email aliases that you can use as a replacement for your real address.
Proton plans on making its password manager open source once it’s released to the public and is also offering up to $10,000 in rewards for security researchers who can find vulnerabilities within Proton Pass and its other products.
So, it seems to tick all the boxes, and it just needs to still publish a browser extension for Firefox. But it is 2023 and the world is in the process of starting a migration away from site passwords, to using passkeys. So one hopes that this planning is also in the works for Proton Pass.
See https://www.theverge.com/2023/4/20/23691097/proton-end-to-end-encrypted-password-manager-e2ee