I understand this is the revival (by another developer) of the original extension, which no longer works on the new FF add-on platform.

I was quite happy to find it, as this was one of my most useful extensions. And when I ran it, the interface looked the same. But it didn't work. Then I found out I had to install another program _and_ a codecs package. Well, thanks anyway, but I'll just copy YT links to one of the online converters... It's simpler, and seems safer.