Well, there is nothing vague here: FTP is a cleartext protocol, and we're migrating towards protocols that provide integrity and encryption.
Sometimes I think it's a generational thing. I find it hard to accept this, growing up with testing all protocols with Telnet and so on. But unfortunately the Internet has changed a lot, and especially bad and unscrupulous people learned how to find all possible and sometimes very creative ways to abuse whatever had been created in the past. So I understand that cleartext POP3, IMAP, SMTP and FTP authentication should go away.
Anonymous FTP is a slightly different beast though. Security-wise, it has the same weaknesses as regular HTTP. But nobody is removing HTTP support from web browsers (yet). So I'm a bit sorry to see it removed from FireFox. There are many better things to copy from Chrome.