Firefox 135 have been released and now you can finally use FIDO2 key to login without password!
Previously you needed Chromium-based browser for this to work. To use this feature, go to Settings -> Security -> Log in with passkey -> New passkey. After adding a key, ensure that it says Used for Encryption:
After this you can logout and try to login again, but instead of entering your email and using classic flow, just click Log in with passkey:
Choose hardware key instead of other methods, enter PIN and your are inside your vault without entering your master password! It doesn't loosen any security, Bitwarden just decrypts your vault using secret from the key. Without having a key and PIN it's not possible to log in.