Here is a comparison chart between Firefox 4.0 Beta 3, Chrome 6.0 and Internet Explorer 9 Beta. With the New hardware acceleration it seems that IE9 is ahead than the other browsers. Ie 9 can warn you if any of the add-ons slow down the startup, with the time that add-on is taken. You may disable the add-ons to improve the startup time.

View the entire chart here