There's absolutely nothing wrong with copying a good idea and executing it correctly. Follow Chrome's separate development channels, Mozilla has released the first channel, Aurora. The idea behind this all is a much more accelerated release, where Firefox 4 took too long before being released.

Besides the cutting edge nightlies, which are released, well nightly, there is now an Aurora channel, which contains slightly less unstable builds. The advantage of this channel is that it's more stable than the nightlies, but still contains an early preview of things to come in the next Firefox release.

After Aurora comes the beta channel, which is not yet ready, and of course the final end product. The idea is that trunk is the main Mozilla central channel is never blocked from new features, while Aurora and Beta channel allow for stabilization of the eventual end user release.

For now Firefox 5 has made it onto Aurora. Being more raw than other releases, this build caries the Aurora name, while official Firefox branding starts in the beta channel. Currently this release looks a lot like Firefox 4, but contains a lot of fixes that just didn't make it.

Let hope we'll see awesome new stuff in the coming weeks! You can try the Aurora channel on your own risk =)