[MxxCon]

When ftp client is in passive mode(sends PASV command), it asks ftp server for IP:PORT to which to connect for data connection.
When ftp client is in active mode it sends PORT command which tells ftp server to which IP:PORT it should try to connect for data connection.


Unless a user has a smart enough router that monitors and understand FTP connection's commands, or if FTP encryption is in play, they need to manually go into their router's configuration and manually forward a range of ports which would be used for FTP data connections. Then they also need to configure FlashFXP or any other FTP client to use that port range.


To save users the hassle of doing all that, server admins who are generally more savvy configure necessary things on their end and tell their clients to just use PASV mode.


Alternatively, switch to SSH/SFTP protocol which is both, encrypted and doesn't need any extra open ports to work. FlashFXP supports this as well.