Oh Yes, I am biased !
I love Google Chrome and believe that it is the best browser ever built. Now, here is a good review about Firefox 4 from  WebworkerDaily.com.
They found that even when firefox 4 has made improvements in terms of speed, it is still way slower than Chrome and Opera.
After testing with WebKit’s SunSpider, and  Mozilla’s Dromaeo testing suite, the results were not so impressive for firefox 4 when compared to Chrome, Opera and Safari 5. Testing was done on my 2.53 GHz Intel Core 2 Duo MacBook Pro; only the major Mac browsers were tested. Please share if anyone here has a better test results from a windows PC.
Please read the full review here. So firefox guys, better luck next time !