There are lots of URI schemes in use. Firefox removing support for FTP doesn't mean that you can no longer open FTP links from Firefox, it just means that they'll need to open in another client. I don't see how this breaks the web.
I tried chrome on an ftp:// uri, and it just does nothing. I suspect because it was the Windows default app for ftp uri's, then they dropped support, but that didn't change the mapping in Windows.