I'm sure attitudes like this — insulting people and excusing bugs based on arcane technical reasons rather than fixing them — have been contributors to the growth numbers in Firefox's market share...
The fact that Firefox supported ftp:// links was a quirk of its evolution. _A_ browser needs not to support ftp, news, gopher, tel or any other scheme. It may, but it doesn't have to. So Firefox not supporting ftp:// anymore was a moronic design decision on their end, granted, but it is, technically and objectively, not really a _bug_.