Himitsu от Drew DeVault

This add-on provides an integration between the Himitsu secret manager and Firefox. Included is support for storing and auto-filling passwords for your web account, alongside other details such as your username, email, or other details for each service. This add-on implements the Himitsu proto=web protocol.

This add-on requires a native messenger component, which should be installed from your system package manager, or from source via himitsu-firefox. The user should install and configure Himitsu itself separately as well.