NetVideoHunter is a Firefox add-on (extension) that helps you to download videos and music from almost any website. Download for example from: Youtube, Facebook, GrooveShark, Metacafe, Dailymotion, Veoh, Vimeo and many more.
It detects the videos that you are watching, so after watching a few videos you can open the NetVideoHunter window to download all the videos you recently watched. Also it has a built-in video player so you can preview the video before downloading or just use it when the player on video site isn't working properly.
For YouTube videos it allows you to choose from different qualities to download when they are available.
What's new in this version:
Fixed YouTube (VEVO too), Grooveshark