I get a proxy squid error wanting authenticiation every time I load firefox

Whenever I try to load up firefox I get a dialogue box wanting me to enter a username and password, with this message: The proxy proxy.brighton.ac.uk:80 is requesting a user name and password. The site says: "Squid proxy-caching web server" The laptop I am using was my partner's when he was at Brighton Uni (but he finished his course there over three years ago!) I'm guessing that the code brighton.ac.uk relates to his password for Brighton Uni but I'm puzzled why firefox wants this. I tried uninstalling and reinstalling firefox - same thing was still happening. By a fluke, I am currently on a part time course at Brighton Uni and have a username and password so I have been entering that to get into firefox - without that I wouldn't be able to use firefox at all. I have also tried clearing the history - that just forced me to enter my Uni password again. Any ideas how to stop it?