I use this add-on to Firefox all the time. Many videos are difficult to follow with just one watching. With this add-on, I can watch on any of my computers; even without internet connection. This is most helpful when I am working in my shop.

Update 11-21-2021 I am still using this plug-in and I still LOVE it.

Update 6-7-2022 This is still a great add-on. I use it all the time.