Overlay extensions

This is an archived page. It's not actively maintained.

This page contains links to documentation for the approach to developing extensions for Gecko-based applications which uses:

  • XUL overlays to specify the interface
  • APIs available to privileged code such as tabbrowser and JavaScript modules to interact with the application and content.

Before Gecko 2.0 was released this was the only way to develop extensions. Now there are two alternative techniques: restartless extensions and Add-on SDK-based extensions. The privileged JavaScript APIs described here can still be used by the newer techniques.

XUL School

XUL School is a comprehensive add-on development tutorial, focusing on Firefox extension development but mostly applicable to other Gecko-based applications.

More resources

Setting up your environment
Setting up the application for extension development.
Tutorials and reference for the user interface language used by XUL extensions.
Code snippets
Sample code for many of the things you'll want to do.
Installing extensions
How to install an extension by copying the extension files into the application's install directory.
Firefox add-ons developer guide
A guide to developing overlay extensions.
JavaScript code modules
JavaScript modules available to extension developers.
Extension preferences
How to specify the preferences for your extension that will appear in the Add-ons Manager.
Frequently Asked Questions
Common issues with extension development.
Extension packaging
How extensions are packaged and installed.
Binary Firefox extensions
Creating binary extensions for Firefox.