Earlier quoted context omitted.
Firefox has consistently been shown to use less RAM than all other browsers: http://media.bestofmicro.com/L/5/390857/original/memuse.png
Not only that, it's faster as well. Try closing a session of Chrome with 20 tabs open and then reopening it. On both Windows and Linux, Chrome can be extremely unresponsive in this scenario. FF lazy loads tabs so doesn't care to reload everything in the background when you restart your session.
I've noticed the reverse with Firefox, closing an instance with 20 tabs takes quite some time. However I've yet to notice Chrome take any time in opening 20 tabs.