Now, let me state up front i am no LAMP or Firefox bigot. For better or worse i am an MS fan, already having converted my household to Vista and OneCare. However...having used IE7 since the early betas i'm afraid to say that Firefox is by far the most usable, quicker browser. Although my evidence is anecdotal (i work and consult with many other developers,project managers, business analysts who all for the most part corroborate my theory), IE 7 is confusing on a very basic level..
OK, i have a widescreen, so these screenshots look worse than on a normal monitor. But hey, wasn't Vista developed with widescreen in mind (sidebar gadgetry etc.)? Anyway, i've marked the key web navigation elements in red below. Note how in IE 7 the back and forward buttons are standalone, but if you want to Stop or Refresh the page you have to go to the right of the address bar. And if you want to go home, you have to go underneath to the tab level, mmm.
I won't even mention the fact that MS broke all previous design and decided to hide the menu navigation. OK, you can show it, but then it doesn't appear where you would expect it at the top, but strangely nestled between the address bar level and the tab level. It just looks well, awkward...
All this would be almost forgivable if like most MS applications you could tinker with the menus, but lo and behold for some strange reason you can't do diddly except hide and show things, the position of everything is fixed, damn!
Contrast this with Firefox, which places all the key navigation elements right next to each other, and logicall places the menu bar at the top were it belongs. You can drag stuff about levels and the whole experience (particularly on a widescreen) is so much more pleasant.