Firefox slow, throws up script errors and crashes - Windows XP

I just installed Portable Apps suite for the first time on a 4GB hard drive. I have tried to run Firefox and each time it takes about 5 minutes to start up and before it finishes loading it states that it cannot run a script if I continue it eventually loads but then crashes. I just tested it on Windows Vista and Firefox works fine, it only fails on Windows XP. Any suggestions?