XUL

XUL Tutorial
A guided tutorial that will help you get started with XUL, originally from XULPlanet.

XUL (XML User Interface Language) is Mozilla's XML-based language that lets you build feature-rich cross platform applications that can run connected or disconnected from the Internet. These applications are easily customized with alternative text, graphics and layout so they can be readily branded or localized for various markets. Web developers already familiar with Dynamic HTML (DHTML) will learn XUL quickly and can start building applications right away. Open XUL Periodic Table in Firefox or another Gecko-based browser to see some XUL demos.

Documentation

XUL Reference: XUL elements, attributes, properties, methods, and event handlers.

XUL Controls: A quick list of all of the available XUL controls.

XUL School: A comprehensive tutorial on Mozilla add-on development.
The Joy of XUL: Describes the key features and components of XUL.

Menus and Popups Guide: A guide on using menus and popup panels.

Template Guide: A detailed guide on XUL templates, which is a means of generating content from a datasource.

Drag and Drop: How to perform drag and drop operations.

Overlays: Overlays are used to describe extra content for the UI. They provide a powerful mechanism for extending and customizing existing XUL applications.