Run native applications inside Xul panel

What little documentation I can find about Xul panels is, unfortunately, not specific enough, so I figured I'd better ask this  in here before attempting many more things that might not be possible by default (therefore turning into a frustrating nightmare). 

Essentially, I want to launch a nsIProcess inside an existing Xul panel. 

The reason I want to do this is that Xul panels are just way more flexible than standard application windows. They can have any shape and transparency isn't an issue at all. 

Part of my little project aims to put tools like Libre Office or Xterm inside such Xul panels, to give them a common look and feel. Kind of like a window manager, just easier to implement and more flexible from the get go.

Has anyone attempted this before and could, thus, offer helpful insights?