This sounded exactly like what I Unfortunately, it appears to do... nothing. There are no instructions as to how to use it, so I assumed there would be an icon to click on to download a video when watching. Nothing. No icon, it's as if the extension wasn't even added. I enabled it and gave it full permissions on firefox but it's as if it's not even there.
Sadly, I'm uninstalling and going back to my search for another video downloading solution.