It's available from 58 (so, not current release) and you have to explicitly enable it in `about:config`. Search for "security.webauth" and enable what you would

It's available from 58 (so, not current release) and you have to explicitly enable it in `about:config`. Search for "security.webauth" and enable what you would like. With that method, you can successfully login to GitHub and other services using U2F. Unfortunately, not Google, because Google doesn't check if Firefox has U2F support or not. Instead, it makes the assumption based upon the browser agent.