Linux Passkey Manager od TinyBrickBoy

Linux Passkey Manager adds native passkey support to Firefox on Linux, where no built-in platform authenticator exists. It works on any website that supports the WebAuthn standard and requires no additional software or hardware.
When a website asks you to create a passkey, the addon generates a P-256 key pair directly in your browser using the Web Crypto API, stores the private key locally in your browser profile, and returns a valid WebAuthn attestation to the website. When you sign in with a passkey, the addon finds the matching credential, signs the server challenge with your stored private key, and returns a cryptographically valid assertion without sending any data to external servers.
If no passkey is stored for a website, the addon stays completely silent and lets the browser handle the request normally. A small confirmation dialog appears only when a passkey action is actually available, automatically adapting to your system's dark or light mode. Through the toolbar popup you can view all saved passkeys, see when they were created and how often they have been used, and delete them at any time.
All private keys are stored exclusively in your local browser profile and never leave your device. The addon has no external dependencies, collects no data, requires no account, and makes no network requests of its own.