Support for extensions using XUL/XPCOM or the Add-on SDK was removed in Firefox 57, released November 2017. As there is no supported version of Firefox enabling these technologies, this page will be removed by December 2020.
Add-ons using the techniques described in this document are considered a legacy technology in Firefox. 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.
Starting from Firefox 53, no new legacy add-ons will be accepted on addons.mozilla.org (AMO) for desktop Firefox and Firefox for Android.
Starting from Firefox 57, only extensions developed using WebExtensions APIs will be supported on Desktop Firefox and Firefox for Android.
Even before Firefox 57, changes coming up in the Firefox platform will break many legacy extensions. These changes include multiprocess Firefox (e10s), sandboxing, and multiple content processes. Legacy extensions that are affected by these changes should migrate to use WebExtensions APIs if they can. See the "Compatibility Milestones" document for more information.
A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.
This page lists practical hands-on articles about how to accomplish specific tasks using the SDK.
- How to install the jpm tool, which you will use for developing add-ons.
- Some pointers for fixing common problems and getting more help.
- Getting started
- Walkthrough of creating a simple add-on with the SDK, using jpm.
- Get the list of open tabs
- Use the tabs module to iterate through the currently open tabs, and access their content.
- Modify web pages based on URL
- Create filters for web pages based on their URL: whenever a web page whose URL matches the filter is loaded, execute a specified script in it.
- Modify the active web page
- Dynamically load a script into the currently active web page.
- Log messages to the console for diagnostic purposes.
- Creating reusable modules
- Structure your add-on in separate modules to make it easier to develop, debug, and maintain. Create reusable packages containing your modules, so other add-on developers can use them too.
- Unit testing
- Writing and running unit tests using the SDK's test framework.
- Chrome authority
- Get access to the Components object, enabling your add-on to load and use any XPCOM object.
- Creating event targets
- Enable the objects you define to emit their own events.
- Listen for load and unload
- Get notifications when your add-on is loaded or unloaded by Firefox, and pass arguments into your add-on from the command line.
- Using third-party modules (jpm)
- Install and use additional modules which don't ship with the SDK itself.
- Writing localizable code.
- Mobile development
- Develop add-ons for Firefox Mobile on Android.
- Add-on Debugger