Clean, minimal, easy on the eyes and simply great looking in my opinion.
Note that you can get this look on Android right now (both mobile and tab) by downloading the
Aurora build of Firefox.
Also with this screenshot, This start page has just been implemented in the newest Aurora build for Windows.
Mockup image shown by Mozilla.
Firefox startpage in current Aurora build.
I've also had a peek at the UX Nightly build for Windows, Australis as shown in the first image above is slowly being implemented with each build released. This is the biggest UI change taking place since Firefox 4.0.