An online copy of O'Reilly's 2002 book Creating Applications with Mozilla. It focused on pre-1.0 versions of Mozilla, so details about the application structure has changed, but the XUL elements are relatively stable.
Stuart Colville investigates the differences between form.getAttribute('action') and form.action, also the cross-browser differences, when the action is a relative URL. One way returns a relative URL, and the other returns a fully qualified URL.