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:

  1. Open the Firefox advanced preferences in about:config.
  2. Search for "webauth"
  3. Enable (value=True) these two:
    • security.webauth.webauthn
    • security.webauth.webauthn_enable_softtoken
  4. Reload this page and click buttons!