Can't get on Firefox b/c of Proxy settings

Hello!

I'm hoping someone can help me with Proxy Settings. I had a crazy virus that took Malware, Hijack This, Combo Fix AND Spybot to get rid of. I have gotten rid of the virus and reset pretty much of everything BUT...I can't seem to get online. It says that the internet is connected but when I click on IE it says about:blank and when I tried Firefox it says can't connect because of proxy settings.

Can anyone tell me exactly how to adjust Proxy Settings to allow Firefox to open?

I'm using Windows XP.

Thank you,
Marci