Your first extension - Mozilla | MDN
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension
This article walks through creating an extension for Firefox, from start to finish.
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension
This article walks through creating an extension for Firefox, from start to finish.