Porting a legacy Firefox extension
If you have developed a Firefox extension using XUL/XPCOM or the Add-on SDK, this page will help you migrate your extension to use WebExtensions APIs. The standard to build extensions for Firefox is to use WebExtensions APIs. It will be the only type of extension supported in Firefox by the end of November 2017 with the release of Firefox 57.
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.