Addon not working Puntuado con 1 de 5 estrellas

Not working anymore, Firefox 46.0.1, windows 10 x64

Puntuado con 5 de 5 estrellas

That's the add-on I looked for! I hate Firefox' behavior and this addon fixes it. Thank you!

Puntuado con 4 de 5 estrellas

It works as described, but opens tabs only in foreground.
Is it possible to open tabs so, in background, if they are opened in background without this addon?

What do you mean by "background" ? can you describe the steps so that I can reproduce it ?