[X2Go-User] Running application for multiple users

I have set up x2go on an Ubuntu 14.04 machine, and it connects and creates a new session fine. However, when I have the first session running an application like Firefox or Thunderbird, then have a 2nd user log in, the 2nd user cannot run Firefox. He gets a message "Firefox is already running".

I thought I can connect with multiple users to the same host? It would not be useful if I can only have one connection. Or do I need a session broker for that?

Regards Peter