I read a review about this the other day.
They tested ff/chrom/ie using some fancy performance site shizz, which were:
SunSpider JavaScript 0.9.1 - A JavaScript benchmark developed by Mozilla with a focus on real-world problem solving.
V8 Benchmark Suite - A pure JavaScript benchmark used by Google to to tune the V8 JavaScript engine.
Peacekeeper - FutureMark’s JavaScript test which stress-tests features such as animation, navigation, forms and other commonly utilized tasks.
Kraken 1.0 - Another JavaScript benchmark developed by Mozilla. This is based on SunSpider but features some enhancements.
The results were:
1) Chrome 10
2) Firefox (not very far behind at all)
3) IE9 (still shit)