Comparison with XUL/XPCOM extensions
This article is a technical comparison between the WebExtensions technology and “classic” extensions developed using direct XUL manipulation and direct access to XPCOM. It’s intended to help orient people who maintain an add-on like this, and who are planning to port it to use WebExtension APIs.
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.