|Also try, Firefox Safe Mode. That will rule out a lot of things that can cause this error.|
How to Start Firefox Safe Mode WindowsXP:
Since it's not allowing a start at all? You need to start it by Holding Down the Shift Key before you start it.
It should then give you two options;
Start In Safe Mode and Reset Firefox. Try Safe Mode first if Firefox starts ok? Delete any extensions you have added recently. Then exist Safe Mode.
Existing Firefox Safe Mode:
At the top right of the Firefox window click the Red X button, then try starting Firefox again in Normal Mode (Rerun it from it's shortcut)
If it starts ok, the latest extension was the cause.
If it doesn't start, go for a Safe Mode start but this time click the Reset Firefox button. Then its asked you if your sure you want to Reset Firefox button.
It will then run a small Reset Firefox tool, then closes it. It will then run Firefox in Normal Mode for you.
If it still wont start after that it could be your Hardware Acceleration.
Please reply and let us know if our help worked. Your feedback helps others. Maybe you?