Unlike in cases like IRC (where the protocol lost popular momentum to commercial tools) and Gopher (where a sudden shift to a commercial model stopped its growth dead in its tracks), FTP is getting retired from web browsers because its age underlines its lack of security infrastructure.
Some of its more prominent use cases, like publicly accessible anonymous FTP servers, have essentially fallen out of vogue. But its primary use case has ultimately been replaced with more secure, more modern versions of the same thing, such as SFTP.
If FTP’s departure from the web browser speeds up its final demise, so be it. But for 50 years, in one shape or another, it has served us well.
This reminds me of Quinn Norton’s post of the dangers of email and whether we will get to a point where the security issues will force a similar change.