Does exactly one thing and appears to do it very well! It has finer speed adjustments than the defaults in the video player, AND can set the speed to *faster* than 2x! I've tried 3x and it works perfectly, although it's really hard to keep up with for obvious reasons. This addon is such a nice quality of life improvement!

The Popup interface could be improved a bit (increase by 0.1 instead of 0.05 or change it to a slider that goes from 0 to 5), but the extension deserves 5 stars for:
- being open source
- the code is stupid simple and a good example for anyone who wants to look into writing Firefox extensions or js in general
- as a result of the first two points, packaging the extension with changed properties (if you want to) is actually pretty easy.