I've Chrome 12, Firefox 5 and IE 9 installed. Here are my results:
http://www.webkit.org/perf/sunspider/sunspider.html
Ch 354.8ms
FF 294.5ms
IE 296.8ms
(lower is better)

http://v8.googlecode.com/svn/data/benchmarks/v6/run.html
Ch 6645
FF 3145
IE 1934
(higher is better)

http://krakenbenchmark.mozilla.org/
Ch 5927.7ms
FF 6838.6ms
IE 17990.3ms
(lower is better)

All on my four years old notebook. How do you perform? And I can confirm that Chrome simply feels and is the fastest browser. Look into your task manager while playing a flash video on youtube: Chrome consumes half as much CPU power as FF does, although both supposedly use hardware acceleration.

Joey

In chrome go into about:flags and enable GPU accelleration there

Chrome ships with its own Flash player version, which is optimized to work inside of chrome.
Beside that, Firefox has the problem that it is horrible slow (in every way), FF4 didn't made it any better. Thats really a shame because the project started as a better Netscape without being a blown up slow thing, no extensions, nothing fancy. Now it is like a modern Netscape.

About FF and JS, Firefox is more open to new JS features, they implement them already at their draft stage to let developer play with it (dunno if this is also the case for Jägermonkey), while Chrome (V8) and Safari (Nitro) just use the current standard without experimenting with it but trying to be as performant as possible.

Firefox 4 starts up very, very fast for me.

it does when you don't start it the first time. for the first time start, chrome loads about 5x as fast as ff (at least). later on, still twice as fast.

there is no gpu acceleration flag there (except for canvas 2d). i guess it's activated by default (i'm using the beta thingy for chrome, that's why i have 12).

Currently at sunspider js test,

ie9 is fastest followed by firefox 5.

Chrome may seem like it starts up really fast, but it only gives you a empty window that, at first 1-2 seconds(in which firefox also fully boots up), does nothing. Even you can't see the new tab page. It loads that stuff after the window is shown. Firefox does that before the windows is shown.