Peacekeeper is said to simulate a realistic surfing behavior. Workload is created via Javascripts, which are used on almost any website these days, and other things. Thus Peacekeeper test the speed of the web browsers so that the user can choose the fastest browser that fits one's own preferences.
Safari is miles ahead of others while Firefox is just ahead IE 7 which is last in the list.
Peacekeeper - The Browser Benchmark by Futuremark Corporation
Peacekeeper: Futuremark introduces web browser benchmark - Peacekeeper, Futuremark, Browser Benchmark, - PC Games Hardware