In 12.04 and later, Citrix Receiver doesn't play well with Unity. AT ALL. Even in fullscreen mode, Unity keeps wanting to grab focus. There are some possible fixes, but they don't do it for me completely. (internal note: what about this?)

One solution is to create a new session on Ctrl-Alt-8, run it under XFCE, and run Citrix there.

To do this:

Other ways to run XFCE4 in Ctrl-Alt-F7, and Gnome/Unity in Ctrl-Alt-F8:

More info: [1] [2]