So I bought the book, reasoning that if I never developed a single application for Mozilla I'd still learn a lot about how to set up a cross-platform internationalized GUI architecture. A little lightbulb went off in my head when I saw this figure.

But the whole package is more than just XUL instead of HTML. It's how to connect to pseudo-COM (XPCOM) objects in Javascript with XPConnect. It's data representation with RDF. Native skinability support and via CSS. The scope of the Mozilla project is pretty big.

Type chrome://navigator/content in the Mozilla address bar (to come back, press the back button). Mozilla's UI is rendered with Gecko, which is the same rendering engine that renders web pages in Mozilla. So you can load (and use!) another Mozilla IN Mozilla, infinitely. In effect, Mozilla is a platform for itself.

The only downer is that as far as I know, you can only write XPCOM components (ie. application code) in C++. I'd much rather take the performance hit and use Java so I don't have to worry about pointers, memory leaks, C++ and XPCOM. ACK, what a nightmare. But it would be good practise ... ha

To try out XPFE (the GUI end), I think I might redo an old client-side Javascript project. No XPCOM required.