I use both browsers everyday allongside one another, both browsers I have (at least) 2 windows open (so Chrome 2 and FF 2). All windows have at lease 8 tabs open. I've come to the conclusion that Chrome uses more RAM then FF when having a lot of tabs open, because each tab is another thread, each tab uses at lease 40mb RAM, another result is that your sysload is also higher. No I don't run Windows, nor OSX.