yes - in fact, one of the ports of pyjamas to the desktop actually uses xulrunner. the xulrunner port is the most stable of the three: the MSHTML one has a couple of keyboard-event-related niggles, and the webkit one, one of the developers is being a bit of a twat. if you're interested in the pyxpcomext glue - in how pyjamas desktop joins up with xulrunner, or if you're interested in writing your own declarative pyxpcomext application, here's an article which explains it:
this is a quite different - and i believe much simpler - approach than "standard" pyxcpomext apps, where you have to "register" your app with the mozilla xpcom infrastructure, then create a xulrunner shellscript wrapper (based on run-mozilla.sh) in order to start up the app - it's just such a pain (but has distinct advantages).
personally i much prefer to start from the python prompt, and the article above explains how to do exactly that.