από τον mehtuus (δημιουργός) στις Σεπτ. 28, 2015 · μόνιμος σύνδεσμος

This is because you were attempting to use the System Override as the "default copy method", which unfortunately is bugged and not working as expected. This will be fixed in the next "Official" update that gets posted here to the Mozilla Addons site. The other options do work fine.