> 5.- I dont know what da hell is Gecko. Gecko is the rendering engine of Mozilla. It is a program the interprets HTML and magically paints it to the screen.
The Mozilla browser is Gecko plus a user interface. XUL is a language used to write the user interface. Gecko is the first software in the world that displays near 100% standards compliant web pages. XUL is the world's first text-based, cross platform user interface language. For the first time programmers can change the UI without having to recompile their application.
