Looks great but needs XP support. Rated 5 out of 5 stars
Looks nice on Vista/7.
Very buggy if used on XP though. The one major bug I found was when hovering over the back/forward buttons: the "hover image" is about 30 pixels to the right of where it should be.
Since IE9 won't run on XP, this could make a great way to bring at least part of the IE9 look to that platform.
UPDATE: The issue was caused by my toolbar customizations. I had set it to show "Icons and text" since my old theme looked better with it. Changing it back to just icons corrects the issue.
I just tested on XP and I have no issues with the back and forward buttons moving when hovering. I suggest you take a look at your add-ons, and make sure you are using the default Firefox theme.