XUL and Firebird

Now that we've made all of our interface and preferences changes that we can through the browser interface, we can close the browser and start hacking the code. Once you've closed Firebird, browse to the main MozillaFirebird directory and open the subdirectory "chrome". The chrome directory is where Firebird stores all of its JAR files. In these JAR files are packaged all of the XUL, JS, CSS and image files necessary for defining the browser interface, its various elements and how they look and behave. In this tutorial, we will be working exclusively with the browser.jar file.

http://tln.lib.mi.us/~amutch/pro/phoenix/kiosk/xul.htm