Why Firefox takes so long to open in Mac OS X?

When I first boot my MacBook Pro with Core i7, 8 GB ram, and 7200 rpm hard drive running Mac OS X 10.6.7, it still takes a long time (10 or so dock icon bounces) for latest Firefox 4.0.1 to open.

Why is it so slow? Is it something on my part? Or is Firefox just that slow to open? Thanks!

P.S. As a comparison, it doesn't take long a all (a few seconds) for Firefox to open on my Windoze machine.

If you have installed many fonts (font packages), you should disable the ones that you don't use. Also try running Firefox in safe mode (without addons). FF4 should start for about 2-3 seconds.