Firefox rocks. There are so many features that it has that IE doesn't it isn't even funny.
However, password manager? Not on my watch. Much prefer something like
http://passwordsafe.sourceforge.net/Multiple tabbing is something I don't ever want to be without.
Really like the bookmarks toolbar. You can group multiple bookmarks (like NYTimes, CNN, LATimes, Chicago Tribune) together, then click "Open In Tabs" and go away for a few minutes and all your websites have been accessed and loaded.
Works better with 30 than 5. <g> One click....all loaded. Amazing. Does IE have something like that.
If you have a mouse that tends to be right-clicked and moved "all by itself", you might want to disable mouse-gestures. That is, if you rest your hand on your mouse and find yourself moving it around and right-clicking unintentionally, mouse-gestures may not be the next best thing since sliced bread.
If you ever want to scroll-size not only text, but graphics, you need Opera. Neither Firefox nor IE expand graphics. Dithering can be a problem, but it is better than nothing.