Finally I found an mozilla addon which really works to download MP3 or MP4 from youtube easily, this is an excellent addon.

It works perfectly.

Install the addon
go to youtube & find video
click on the cube in top right corner & click on youtube addon
Click on the download MP3 link
Close the pop-up ad and wait until finished
Folder with file will open when you click on it.
If you morons can't find out - go down and buy it!

Doesn't download anything, just opens a spam tab on browser

easy to install and use. it just works. no better way to extract mp3 audio from videos.

ik kan er niet eens in

A extensão abre uma nova guia onde eu posso escolher se quero baixar o vídeo no formato mp3 ou mp4. Quando clico em qualquer uma dessas opções, a extensão converte o formato, mas não baixa nada e o botão desaparece.

Simply useless.

CUIDADO!!!! INSERTA PUBLICIDAD EN LA BUSQUEDA DE GOOGLE. MUY PELIGROSO