EDIT: Unfortunately this once great extension is now defunct. The author doesn't seem to keep it updated anymore. Don't bother with this. Grab "Video DownloadHelper" instead.

The best youtube downloader extension, period. I'm a tabletop RPG GM and I use music from video games for my sessions a lot and the music is hard to find sometimes. So it's easier to just go on youtube and do the conversion myself. The person maintaining this extension is very diligent in updating it too. 5 stars!