I'm a major Firefox user. However, I also use a lot of Google Chrome.
I am a Firefox Alpha tester. This means that I run a version of Firefox that is 2 versions ahead of the official release. At the time of this post, the current official release is Firefox 7. I am running Firefox 9. This means that I have to deal with a lot of potential crashing issues and experimental features, but I don't really mind the risks. Firefox Aurora (as they call this version) is, in my opinion, much better than Google Chrome. It feels a lot faster, a lot more streamlined, and a lot more powerful.
However, I also use Chrome for a lot of my secondary accounts and other needs. Being a web developer, administrator, and webmaster of Pokemon Dungeon, I have many accounts that I have to often use simultaneously. Having Chrome open allows for me to be logged into a bunch of the same sites that I use in Firefox, but with different accounts.
I have nothing against Google Chrome, as I really like their interface and capabilities. However, Firefox just feels much better than Chrome.