When I click on one of the green download buttons, nothing happens. For some videos. For others, it works fine.

Why absolutely nothing?? At least sho what's the matter. Maybe it's fixable from the user's end. A silent fail, where ab-so-lu-tely nothing happens, is just bonkers.

I downloaded the add-on based on popularity. It did not detect the video on twitter. Nor does it accept suggestions as to where the video frame is.
I suppose it is Windows oriented (I use it in linux).

Maybe a future update will resuscitate it, but right now, as other reviewers have noted, it just displays "No videos found. Why?"