There is Firebug and YSlow that you can use via firefox. I use these all the time.
Firebug:
addons.mozilla.org/en-US/firefox/addon/1843
YSlow:
addons.mozilla.org/en-US/firefox/addon/5369
WebDev:
addons.mozilla.org/en-US/firefox/addon/60
The last one is not too bad either. But the two you would like to use are the Firebug and YSlow. YSlow shows you not only what takes how much time to load, but also ways to help improve the speed with tips and tuts on how to do this.
I hope that helps.
Peace,
Sarrene'
Edit: Looking at your site it is not too bad, Seems to slow down at a few graphics, but that is about it.This page has 4 external Javascript scripts. Try combining them into one.
This page has 4 external stylesheets. Try combining them into one.
This page has 76 external background images. Try combining them with CSS sprites.
Do remember that most sites do NOT get an A or B, but you can see what is slowing things down. Of course, your isp will make a huge difference. For me, it seems to load fairly fast after the first time (thanks to cookies and cache of course.) Also, Check out your js. I have noticed that often times, a spread out series of js files or an uncompressed js file can slow things down quite a bit more.