I personally don't expect anything to come out of the UI design for Firefox next. Remember all those concepts that came out for Firefox 4 that looks really good? Now compare that to what it actually look for FF4+, it's garbage. It's just a bunch of XUL horribly squashed together. They should just disband the UX team. Hell, if it weren't for BoneyardBrew and SoapyHamHocks, I don't know if I would even be looking at Firefox right now.
If you compare it to the Mockups for Firefox 4, it's pretty darn close. The only difference is really the tabs being "square" compared to how they were more rounded on the edges.
New rounded tabs IMO look great! The default ones we have now IMO are way too plain.