Version: (using KDE 4.2.4) OS: Linux Installed from: Mandriva RPMs As confirmed by Thiago (https://bugs.kde.org/show_bug.cgi?id=155707#c140), FTP sites can't be accessed through an HTTP proxy. If you try to, a popup shows up : "URL can not be listed". I can only test here with an NTLM authenticating proxy, but the problem may affect other types of authenticating proxies or even non-authenticating proxies.
See also bug #177583 and bug #195085.
Marking as duplicate of the oldest bug report. *** This bug has been marked as a duplicate of bug 177583 ***