This is the "RPID is Origin w/ Firefox attestation mode" checker, not the W3C U2F mode. It's for Firefox <54.
To use this to test Web Authentication support in Firefox, do the following:
- Open the Firefox advanced preferences in about:config.
- Search for "webauth"
- Enable (value=True) these two:
- security.webauth.webauthn
- security.webauth.webauthn_enable_softtoken
- Reload this page and click buttons!