I gave up on Firefox nearly a year ago, and switched almost completely to Google Chrome. However, I use the Developer Release version, not the beta version or release version. The advantage to the Developer builds is that you get more features.

I find it to be quite good, but there are one or two sites I've come across that just don't seem to work right in it, at which time I fire up Safari.
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The Graphic Mac - Tips, reviews & more on all things OSX & graphic design.