Reviews I've read say Chrome get the nod over Firefox in performance. My problem is Chrome is a product of Google and Google tends to be on the wrong side every time a privacy issue comes up.
Not just that, but Google has seemed to have really slowed down for me. It takes a while for Google to load (and search), it takes a really, really long time for Gmail to load. Yahoo and yahoo mail, in contrast load very quickly (even though Yahoo's main page is laden with graphics and such). And I'm using Chrome. I remember back when Google main page loaded extremely quickly. It doesn't anymore.
I'm going to try FF4. I switched to Chrome after FF3 because it was just too slow and crashed a lot.