Actually, I disagree. Firefox uses 150 meg of memory on mine too but when I have 25+ tabs up. When I used IE, it used 250 meg+ and then 30 - 50% of my 1 gig RAM. At least with Firefox it goes quick for that, IE was incredibly slow...
Jake, I agree completely. On my PC, wIE7 uses 500+ megs of my 1280mb RAM, admittedly the rest of the specs on my pc suck, but it freezes all the time. Firefox, however, with ABP, Stumble, 40 tabs and so on, it works just about fine, and doesn't eat more than 400mb of my RAM, and shares the processor in a nice friendly manner