Hello! Our help will be more effective, if you copy and send us info about your browser: 
http://en.savefrom.net/user.php?info=1 
We'd also need some links you can't download (to test them). 
For the better understanding it'll be great to see a screenshot with the error. 
We are waiting for your reply, and thank you for contacting us Savefrom.net Team!

Hello, Unfortunately, we don't fully understand you... please. provide us with more details regarding the issue.

Thank you for using our extension SaveFrom.net Helper

Hello, please, send us more details regarding the problem.

Hello, please, send us more details regarding the problem.

Hello, there is no technical possibility.

In order to download MP3 from YouTube you need to instal our Ummy Video Downloader. This useful tool will help you download
both HD and MP3 from YouTube: http://videodownloader.ummy.net

¡Hola! Nuestra ayuda será más efectiva si copia y nos envía información sobre su navegador y de la extensión Savefrom.Net:
http://es.savefrom.net/user.php?info=1
Para tener mayor idea del problema, será de gran ayuda ver una captura de pantalla en donde se muestre el error.

¿Se descarga a través de la extensión SaveFrom.net Helper o del sitio web SaveFrom.net?
Esperamos su respuesta, ¡gracias por ponerse en contacto con nuestro equipo Savefrom.net!

Hello, please, send us more details regarding the problem.

Hello, the link that you sent does not download any of our services, especially since the link leads to a closed group.