ftp://ftp.oreilly.com/pub/freebooks/mh/index.htm is an example of an HTML web page served over FTP with relative links. It's worked fine for 25 years (though I bet 25 years ago the URL was only ftp://ftp.ora.com/pub/freebooks/mh/index.htm, which still works) with very little effort on the part of the redoubtable crew at O'Reilly and Associates. Now it's being broken. Intentionally. For no good reason.