Why are you messing with everything, Mozilla? Why are you breaking the UI metaphor? With the tabs on the top, all the elements under it are made to appear a part of that tab. There's no reason that I can see for the tabs to be on top. It doesn't look pretty, it takes extra pixels to render the smooth curve where the tab meets the next bar. Even if I'm insane and it's the same width, it still looks awful.
I've got five HD screens, and everyone is taking the tablet friendly, ergonomic approach. I want consistency. Please stop breaking everything. You're the last good browser, Firefox. Don't ruin it.
Please bring back: tabs on bottom, the permanent forward button, the refresh button, the bottom bar anchor, and the separate back button.