Well... it's been a day since it installed itself and it's alright but I'm certainly not digging the new tab design. Just seems awkward and like it might be taking up more space (but that's probably just an optical illusion). The new menu is cool but not really anything particularly helpful. I also think there are some bugs. It seems to be tripping over it's wang more than the previous version.
 
Meh. Not annoying enough to make me use an addon or whatever to switch it back though.

I'm still using Win XP. I haven't tried the "Classic Theme Restorer" yet, but I did clean up many of the changes that Firefox dropped on us :
 
From the desktop, I right clicked on the Firefox icon ->Properties->Compatibility, then checked the little "disable visual themes" box. This restored the colors on the top band of the screen (which brought back the minimize/restore/close boxes on the top right), and made the folder tabs much easier to see and handle.
 
I don't know what you would need to do to accomplish this with newer versions of Windows, the options available when selecting "properties" has evolved with the Windows version releases, and disabling visual themes from an external source might be trickier than it is in XP.