Usually Firefox will connect to the network using your system settings, which you can find either in IE or in the Windows Control Panel, Internet Options, on the Connections tab under LAN Settings.

Firefox can use a different connection method to take advantage of an intermediary. For example:

• Security software on your PC which intercepts and cleanses your web traffic
• Private VPN service that sends your requests out through a different device so it can't be tracked back to your ISP

However, these settings also could be used by an attacker to divert you away from the "real" internet to one where fake sites can be interposed to capture your passwords or other personal information.

Not sure exactly what is happening in your case, but if you made a note of the earlier settings, that would be helpful in investigating further.

On Windows XP you usually need to select the no proxy setting, especially if the default "Use the system proxy settings" isn't working properly.

• Tools > Options > Advanced > Network : Connection > Settings