Chrome uses massive quantities of memory per tab. With just a few tabs open it can use over 2GB of memory. It's far from being "light on resources".
Firefox is well known for being bloated and slow. If you have to choose between the two, Chrome is probably the best choice at this point as web standards are leaning towards supporting webkit more.
However the most obvious choice might be Opera. It runs very well on low-end systems, is faster than Firefox, and uses less resources than Chrome. Unless there's a specific reason you don't want to use it, give Opera a spin.