I've created a mozdev project for the Semantic Web stuff I'm doing. Nothing much to see yet, although you can look at the code and try compiling it yourself if you like. The client uses XUL and XBL and so on. It also uses a custom native XPCOM component written in C++. I used RH8.0 Linux gcc 3.2 to compile. Since I don't have any other compilers, I can't test if it works anywhere else. I'll write some actual documentation soon.