eeeeeeep! Don't do that! If you're having trouble accessing something using Firefox, I don't see how it could be IE's fault. Unfortunately, I've never used the MSN web interface and the error message you're getting is a very generic one so I'm reeeeeeally not much help here.

The absolute best I could find is this UK Hosting/University connection question where someone was getting the same generic error message. For more help than this, you must apply to the Great Oracle of Über-Geekdom Herself.