I haven’t made any scientific comparisons, I only share my experience. I’ve been a devoted Mozilla/Firefox user for many years. My current workhorse is an AMD Phenom Quad core box with 8GB RAM and it flies.
I tend to keep 40-60 tabs open, on average. I can run the latest Firefox on this box and it will have severe performance problems (the screen turns grey, desktop unresponsive) even with nothing else running. I have to restart Firefox 3 times daily. It takes a long time to reload, so this is a major inconvenience.
I am now running Chrome with 42 tabs, as well as Thunderbird, Gimp, Pidgin, 5 terminals, and 2 virtual machines (Ubuntu 10.4 using QEMU and OpenSuse 11.2 using Virtualbox 3.1) – all this on a fully pimped-out Compiz 3D desktop on a 24″ display – with outstanding performance from Chrome.
I love the Fox, but until it gets its act together, I’m using Chrome.