I've got tired of Firefox 3.x loading time. It's over 15 seconds even on 4gb of RAM in Windows. Then I've found this useful link:
This is a small program that starts when you login and loads in RAM some code from Firefox. So when you start Firefox, it will take up only 4-5 seconds top (in my case) until window pops out completely usable. Pretty neat.
Also you can execute firefox.exe with Prefetch 1 parameter. Edit your shortcut and execute it like
C:\Program Files\Mozilla Firefox\firefox.exe” /Prefetch:1
Works in XP very well.
Tiny and free. Makes a difference. Anyway, I've started using Google Chrome for it's speed. I miss some addons but I'll wait for Firefox to fix some issues first.