[Nyx]

At first i didn't understand what the difference was so I Google'd it and this is what I found:
Firefox Nightly is an Alpha
Firefox Aurora is a Beta
Firefox is a release.

After every new update, Nightly turns into Aurora, Aurora turns into the Release and then they make a new Nightly for the next update. So what you are seeing right now in Aurora is what is to come in the next Firefox update, just buggier.