IMG problems in Firefox

While having some time to spare, I wanted to put some common JavaScript functions together in a library, but everything didn't work out the way I had hoped. At work everything went fine in all web browsers I had access to – IE 5.5, IE 6, IE 7, Firefox 1.5, Netscape 8.1 and Opera 8.5 – but when testing at home, nothing worked in Firefox. Nothing I did seemed to help.