Search for Citrix Workspace app for Linux Web client. They have a deb
package. You should figure it out yourself. We are not supposed to go into
detail here.
It seems Citrix has issues with mouse integration. My search yielded various
issues having black cursor rectangles. Some solutions involved adjustments in
the remote desktop (Win registry), some suggested applying 'DisableXRender=1'
in the local client configuration (ini file under $HOME).
Other than that, it's impossible to say without installing and using the
proprietary client.
Maybe you could use another way to connect (other than a web client). There's
VNC software in Trisquel that can connect to remote desktops (Vinagre).
