YouTube Downloader от sachagd

Firefox extension that allows you to download YouTube video and playlist in mp3 or mp4 files. You can also select specific parts of the video, choose the resolution and even add automatically your mp3 files downloaded to your iTunes library.

This part is the firefox part of the extension. It will not work if you don't install the corresponding local part on github (https://github.com/sachagd/YoutubeDownloader).