IE9 is a little faster than Firefox6 in Speed Reading performance test but so less
http://ie.microsoft.com/testdrive/Performance/SpeedReading/Default.html
Score (less better) | Windows Size | Test Date | |
IE 9.0.8112.16421CO | 22 seconds | 1858x1024 | 8/21/2011 |
Firefox 6.0 | 23 seconds | 1858x1016 | 8/21/2011 |
Conclusion: IE 9 maybe a little faster, but consider the Firefox more memory footprint saving and cross-platform and so many extension and plug-in. I still prefer Firefox as my primarily browser.