Takes 1 to 2 minutes for firefox to start for the first time

I have installed portable firefox on my usb chip and it was very slow starting. So I moved the program to the c drive. Still the first time I run a browser command it takes a minute to 2 minutes for firefox to start. My usb is a 1.1. I have windows xp pro installed with webroot spyware sweeper and bitdefender anti virus. Is there any way to speed this up? I did install fasterfox too, which did nothing for this first time starting problem. Sure would appreciate any input on this. Thanks In Advance