Firefox Developers a plan to completely stop supporting the FTP protocol, which will affect both the ability to download files via FTP and view the contents of directories on FTP servers. In the June 77 release of Firefox 2, FTP support will be disabled by default, but about:config will the “network.ftp.enabled” setting allows you to return FTP. Firefox 78 ESR builds support FTP by default turned on. In 2021 completely remove FTP related code.
The reason for discontinuing support for FTP is the insecurity of this protocol from modification and interception of transit traffic during MITM attacks. According to Firefox developers, in modern conditions there is no reason to use FTP instead of HTTPS to download resources. Additionally, Firefox's FTP support code is very old, poses maintenance challenges, and has a history of revealing a large number of vulnerabilities in the past. For those who need FTP support, it is suggested to use external applications attached as handlers for the ftp:// URL, similar to how irc:// or tg:// handlers are used.
Let us recall that earlier in Firefox 61, downloading resources via FTP from pages opened via HTTP/HTTPS was already prohibited, and in Firefox 70, rendering of the contents of files downloaded via ftp was stopped (for example, when opening via ftp, images, README and html files, and a dialog for downloading the file to disk immediately began to appear). In Chrome also plan to get rid of FTP - in The process of gradually disabling FTP support by default (for a certain percentage of users) has begun, and Chrome 82 is scheduled to completely remove the code that makes the FTP client work. According to Google, FTP is almost no longer used - the share of FTP users is about 0.1%.
Source: opennet.ru