http://www.itworld.com/software/266362/whats-fastest-browser-maybe-youre-measuring-wrong?page=0,2
In their official stable versions, IE9 and Chrome used the most memory in the 15-tab scenario. (Expect that number increase drastically if you're the type who swiches between 40 or more tabs.) Firefox 10, however, beat them all: It consumed around half (!) of the memory that the others needed in this scenario. Although its basic resource usage ran at 68 MB, it scaled quite well up to 218 MB when loading five tabs.