@Photor Frustation! Wanted to play with it - but I always end with a gray screen, no mouse, no keyboard, no chance to quit. I always have to shutdown the VirtualBox-machine. I have no idea, what happened. I have updated VirtualBox in Archlinux host, but that should not affect the FreeBSD in the box. I have already checked against FreeBSD handbook - found nothing special. No idea at the moment.
So. #Xfce under #FreeBSD is up again! I do not know what happened. But I went back with the #VirtualBox to a saved state before the #Xorg installation and set it up again: installed xorg, xfce and slim. Now I can play with the system - #happy