Are you using a password manager other than what comes with the browser?

Just to make sure, please read everything: Type about:preferences#security<enter> in the address box. Look under Logins,

Note: For Firefox v56+ its; about:preferences#privacy Look under Forms & Passwords Or type about:logins<enter> in the address box. +++++++++++++++++++++++++++++++ Turn on Remember Logins. To check the passwords you have listed, press Saved Logins.

Press the Exceptions button and see what's inside.

https://support.mozilla.org/en-US/kb/password-manager-remember-delete-edit-logins

Start Firefox using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

Can you create a new login via the button at the bottom of the left panel in Lockwise ?

• https://support.mozilla.org/en-US/kb/password-manager-remember-delete-edit-logins