I have several hobbies and use tutorials to continue learning about then. I have used Video DownloadHelper for years to help me download the best of them. It downloads seemingly every format of video, although with the newer version of Firefox it needs an extra bit of separate code to help it achieve it, but that's not a problem. I haven't yet found another addon that can do the same.
So now I have a video library of all my most useful tutorials, thanks to Video DownloadHelper. Highly recommended!
P.S. It does lot of other things as well.