Mozilla - From Browser to Desktop Environment?

An anonymous reader asks: "A while ago OEone released a thingy called Penzilla which was basically a Mozilla desktop environment like GNOME or KDE. Everything was written in either DHTML or XUL and ran within the Gecko engine. Recently a new project, Robin was released that is basically a desktop running within Mozilla using XUL as well. There is NetWindows that attempts something similar for more interactive web applications. What advantages would a 100% Mozilla engine desktop hold and what are the disadvantages compared to much more complex environments such as GNOME or KDE? Is a Mozilla desktop possibly more elegant or efficient for the typical user? Is the XUL runtime environment more robust than troublesome C/C++ widgets? It seems like most applications could make the transition as the growing collection of Firebird extensions like ChatZilla and Gnusto and have shown."