Although they share the same version number, this isn't the Nightly-UX build that just came out. There's, unfortunately, no PPA available for that at this point so you'll have to get the UX build straight from Mozilla.
It looks awesome, though.
Firefox Nightly-UX build on Ubuntu 12.04
It's too bad Ubuntu users probably won't get to experience the new Home Tab. We'll be getting the same ol' start page we've been getting all these years.