I have set FileZilla FTP Server. I was able to connect and transsfer files over the LAN and WAN through the command line (telnet, ftp). I am unable to access it through my browser, even though that I have tried ftp://user:pass@ftp. Firefox give me the error "425 can't open data conenction" whereas, internet explorer does not give me any notification, it is just do not work. But, when i observe FileZilla FTP Server, I see that the connections are coming in. What could be the problem?
FTP initially opens a command connection from client to server. The server then opens a data connection back to the client (i.e. in the reverse direction) Firewalls often block incoming connections of this sort.
Passive FTP was developed because of this, in passive FTP the client opens the data connection too.