Rated 3 out of 5 stars
Pretty good for an Experimental 0.1 release, very promising. I have a couple of small problems running Win7 with FF 4.01:
1. With tabs on top in the title bar, the Min/Max/Exit icons are black on black. The icons work if the mouse clicks in the correct location, but I cannot see which is which.
2. The ALT button to temporarily show the menu bar does not work correctly. The menu bar is superimposed over the tab names.
However, the remaining functionality is as desired and gives me the most usable space within FF, even more than Chrome.
A 3 for now, but will reevaluate as bug fixes come out.