If you load the page at the referenced URL you will see a number of A tags of the form <a href="http:file.html">link</a> The author meant this to mean the same as <a href="file.html">link</a> but Mozilla interprets it as <a href="http://file.html/">link</a> i.e. it attempts to contact a host named file.html by HTTP. Of course it cannot find any DNS entry for that host, so you get an error dialog box. It would be nice if, in this situation, Mozilla responded to the failure of DNS lookup by reinterpreting the URL as if it hadn't had a protocol field in the first place. This would cause the page to work as the author intended.
See bug 32966 and bug 22251. This has all already been beaten to death... Marking as duplicate of bug 22251, since that one fits this bug more closely. *** This bug has been marked as a duplicate of 22251 ***