Before microsoft came along with Mozzillas "tabbed browsing" they had nothing good.
They had a simple browser that anyone could make in Visual basic. Now they added a slower version of tabbed browsing....
My emachine has a 2.19 ghz amd 3000+ proccessor, 128 mb video memory, 1 gig of ram..... and when i open IE 7, it freezes for about 6-10 seconds, then decides to load the webpage, it froze everytime i went into hotmail. It has poor security, for say if you ever went to a website for cereals, or something. you get porn popups everywhere that wont close until you press yes, which in return downloads virus's, not only that, but its shit.
Firefox on the otherhand, has better bookmarking, better tabs (easier to navigate), Skins for your likings, the little search bar at the top right (love it), extensions, that arent just little bars going across the top of IE with linkable buttons. Way more security, whether you like it or not. Popup blocked is flawless. multipule profiles for your whole family, so everyone gets different bookmarks, not all together like IE would give. Different profiles gives different possibilities, like everyone can have their own skin, or their own homepage, or their own extensions. All around firefox is best your going to find.
IE is nothing bad to use, its just plainly less secure and less functional that FireFox.
=)