I swap the code and the button does work.
I believe the old version is still in Codecanyon. This is the plugin I downloaded: https://send.firefox.com/download/3659cf7f62/#ehHi5uN9iOGBaxjGI7jgSA
(link will expire on first download or 24 hours, don’t worry!)
That’s why we have this back and forward thing, becuase the “old” plugin is still there.
I gave you a 5 star on the plugin for your support.