I'm a pretty big user of youtube-mp3.org, specifically when it comes to music. This is a great add-on I highly recommend anyone try out.
I only have one small issue, and I'm not sure if it's only on my end. The app runs flawlessly most of the time, right-clicking gives the option to download the video as an MP3.
For some reason, I sometimes have to refresh the page in order for this to show up. It's nothing major, but I hope this could be addressed before more comments saying "the App doesn't work" show up.