Buttercup (Codekunde) by CKdev

Buttercup is a free, open-source password manager. This extension connects Firefox to a running Buttercup desktop application over an encrypted local connection, so you can autofill logins and one-time passcodes without ever copy-pasting a credential.

This is Codekunde's fork of the original Buttercup browser extension, archived by its original maintainers. We maintain it going forward alongside our Buttercup desktop fork.

Features:
Autofill usernames, passwords and TOTP codes into detected login forms
Search entries and one-time passcodes from the popup
Save new logins as you create them
Works with local vaults, Dropbox, Google Drive, WebDAV and other Buttercup-supported storage
No account and no cloud sync of our own — your vault stays where you put it

Requires the Buttercup desktop application (v2.26+) running in the background.