I love the idea! Unfortunately the site I was trying to use it on (mjam.net) didn't seem to think that the *@relay.firefox.com address was an actual email address and prompted me to enter one over and over again.

So for now I cannot give it a better rating, but I will gladly change it if I was somehow mistaken, the issue is not with firefox relay, or the issue is fixed.

EDIT: keep up the good work!