Anatomy of a Firefox Extension

Firefox Extensions are written within the Mozilla frameworking using XUL overlays, JavaScript, CSS, and RDF. Also, XPCom is used to provide support for external libraries including SOAP and XML-RPC and bindings for Python, Perl and Ruby. The XPI format facilitates online installations at a click and simple removals.
See The The Joy of XUL for more information on the technolgies mentioned above.

name.xpi (zip file)
  /chrome
    name.jar (zip file)
      /content
        about.xul
         (about in extension menu)
        contents.rdf
         (integrates overlay info into browser)
        nameOverlay.js
         (logic and functionality)
        nameOverlay.xul
         (scripts/import, interface elements)
      /skin
        /classic
        /name
          anything.png
          contents.rdf (paths to skin files)
  /default
  /components
    name.dll
    name.js
  /defaults
    /preferences
      name.js
    name.ext
  install.js(0.8-)
  install.rdf (0.9+)
   (GUID, name, version, description, etc)

Developer Resources

• Building an Extension - Sixteen detailed chapters straight from the source.
• How to write Firefox extensions - Overview of an XPI in a classic 'Hello World' tutorial.
• Writing Firefox Extensions - Primarily a breakdown of install.rdf but incomplete.
• Firefox Extension Wizard - Easily generate a skeleton extension.
• GUIDGen - Microsoft's tool to generate a GUID for use in your install.rdf file.
• Firefox Extension Development Tutorial - A step-by-step guide providing many examples, explanations, and external references.
• Extension Packaging - An overview of building bundles which can be downloaded and installed by a user.

XUL Development

• XUL Tutorial - Tons of focused information on the XML User-interface Language.
• XUL:Template Guide - All about generating content from an RDF datasource.
• The Joy of XUL - A breakdown of XUL and its supporting technologies.
• Why I use XUL - An informal opinion on the speed and simplicity of XUL development.