I've been using Chrome as my primary browser for almost two years now, but the Firefox 4 nightlies are really getting impressive and it's starting to become a viable alternative to me. The Omnibar extension, superior font rendering, and tabs-on-top address a lot of the common usability complaints and Firefox's JS performance is finally on-par, and in some cases much better (especially where graphics are intense), than Chrome/V8's.

Chrome still has much more pliable tabs, but things are finally looking up again for Firefox, and it's about time.