This is the CR attestation mode checker. It's a work-in-progress.. Code is on Github, though deployment is manual.
You can also load this page on port 8443 to test that alternate ports work for a given RP ID.
To use this to test Web Authentication support in Firefox, be sure you're using Firefox 60 or later.
Relying Party ID to use. "bin.coffee" and "webauthn.bin.coffee" should be the only valid options. Ports, paths, schema and such should be forbidden.