chat web application with xmpp and firewall

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C#

Chat

XMPP

firewall

This is asp.net web application for chatting, developed using agsxmpp and signalR to integrate google chat and facebook chat.

We use these settings for establishing an xmpp connection:

XmppConnection = new XmppFacebookClientConnection();((XmppFacebookClientConnection)XmppConnection).ApiKey = ApplicationKey;
((XmppFacebookClientConnection)XmppConnection).AccessToken = AccessToken;
XmppConnection.Server = "chat.facebook.com";
XmppConnection.Port = 443;
XmppConnection.AutoAgents = true;
XmppConnection.AutoRoster = true;
XmppConnection.UseSSL = true;
XmppConnection.UseStartTLS = true;
XmppConnection.Priority = 0;
XmppConnection.UseCompression = true;
XmppConnection.AutoResolveConnectServer = false;
XmppConnection.ClientVersion = "1.0";

The chat application works fine on machines which are not protected by any firewall, but when we try to access the same app from a firewall protected machine the connection is not established.

What should we do to get 'through' the firewall? Is there something I can do in my code or do the users need to change their firewall settings? How?