Tested on 02/05/2021.
No download button on youtube.com!! So I can only assume that this FF addon is another scam to get your browser data!!

Contains adware

Since there aren't any links to contact the developer anymore, I guess I'll ask here. Will you please explain the purposes of the particular permissions this addon requires? Why do you need to access my data for all websites? Etc.

Doesn't see any videos on Youtube and Facebook

This extension ("Flash and Video Download") injects smartredirect links into regular browsing processes that have nothing to do with the supposed functionality of the extension, so instead of directly going to another page or site, it loads a smartdirect catcher link in-between.
This behaviour should be banned.

If I could give this zero stars I would. This extension DOES NOT work at all, I've tried everything and it STILL remains gray. Don't bother downloading this

Muy Bueno...

Gostei, muito prático.