I’m not looking forward to the new interface much either. There are already plenty of skins out there to make it look like Chrome/Chromium, so why on earth would anybody want to put it in permanently?
If you don’t like it, get the Aurora or Nightly builds, (those are the ones whose feedback influences development most profoundly,) and submit some feedback on the new interface.
On the other hand, it may end up looking pretty good on Firefox; who knows?