Edit: STILL working AMAZING in August, 2021. I have downloaded well over 10,000 videos now with this extension. It is literally the best extension on the Firefox store. Do not listen to any negative reviews, they obviously don't understand how crazily complex making this add-on was, and how well it downloads videos. If you are buying it sololely for Youtube, then just get the license, its fairly priced unlike most software, and the developer made a great product.

An absolutely amazing addon, that the developers have made available to all firefox users free of charge. I've used this extension so many times I've lost count. It work's flawlessly on 99% of videos and sites, and I have to just applaud the developers for contributing to the usability of the internet in this way. Thank you to all the devs!