Swiftfox, an optimized build of Firefox for Linux is pretty good with speed. I am running the 64 bit build of 3.6 and it's cpu and mem usage seems pretty good to me. They have prebuilt binaries, but only for Ubuntu.
Rohit Garg is a senior undergraduate student in the Department of Physics at IIT, Bombay. His interests include, among others, 3D graphics, computational physics, electronic system design, HPC and economic theory.