Firefox will not work

Hello,
I'm having this problem and I have no idea if it is a repeat question.
My internet is connected fine, but for some reason my interent explorer 7 works just fine, yet my firefox will not connect. It keeps saying:

Though the site seems valid, the browser was unable to establish a connection.

* Could the site be temporarily unavailable? Try again later.
* Are you unable to browse other sites? Check the computer's network connection.
* Is your computer or network protected by a firewall or proxy? Incorrect settings can interfere with Web browsing.

I'm on Vista, and I know little about computers so step by step instructions would be amazing. Someone help please!