In this article I'll show you how to create skins and explain the role they play within the Mozilla development platform.
Skin refers to the look or overall style of an application such as a web browser.
The skin of a Gecko-based application is separate from its structure and function because of the way in which the interface is defined. In broadest terms, XUL defines the structure of the application, JavaScript describes the behavior , and Cascading Style Sheets define the coherent look, or skin. By changing the CSS files or pointing to a different set of CSS files entirely, you can change the skin of the application without affecting the underlying structure or functionality. Given the basic structure as defined in XUL and the linking or functionality as defined in JavaScript, the skin is free to express the look of the interface in almost any way it chooses. Alphanumerica's Sullivan Skin.