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We are planning to deprecate the use by Firefox add-ons of the techniques described in this document.

Don't use these techniques to develop new add-ons. Use WebExtensions instead.

If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions instead.

Add-ons developed using these techniques might not work with multiprocess Firefox (e10s), which is already the default in Firefox Nightly and Firefox Developer Edition, and will soon be the default in Beta and Release versions of Firefox. We have documentation on making your add-ons multiprocess-compatible, but it will be more future-proof for you to migrate to WebExtensions.

A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.

XUL School is a comprehensive add-on development tutorial, focusing on Firefox extension development. It is recommended that you read through all of it at least once. While Firefox changes rapidly, the content in this tutorial should be up to date and valid.

Introduction
Basic functionality
Intermediate functionality
Advanced topics
Appendices

The XUL School project was developed by Appcoast (formerly Glaxstar). The project is now published here following its sharing licenses. Its contents have been modified from the original source as necessary.

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 Last updated by: wbamberg,