Stop recognizing FTP addresses
Chrome 81 will disable FTP support by default, and 82 will completely drop support for this protocol – originally planned for Q2 this year but delayed.
Firefox 77 will probably disable FTP support by default (mid this year), and they'll drop it early next year – this was in the news today e.g. here; based on the upstream intent discussion.
I'm not sure if Epiphany can handle FTP, if I type such an address it opens up in a Firefox tab for me.
This means it'll be pointless for us to recognize this protocol anymore (and also to set $FTP_PROXY). Even if the user clicked on it, it wouldn't open up properly in the browser.
Let's remove this from GNOME 3.38, or 3.40 the latest. (What's up with ftps and sftp? Can we drop those, too? I guess so.)