The features seem nice. The integrated to specific sites not so much. I know they say they'll add more video sites. That still means if youre not an established popular site you're basically 2nd class and your users may switch away because they can not use the feature.
That doesn't seem proper for a brower and certainly not one with Mozilla's M.O.
It would be nice if Min Vid would work on every <video> element. That would seem like the right way to implement the functionality.
Additionally, they're looking at supporting any old HTML5 <video> element: https://github.com/meandavejustice/min-vid/issues/331
The intent is certainly not to be exclusionary; it's just a new, experimental project with a small team.
Disclaimer: I work at Mozilla, on Test Pilot.
Why wouldn't you just make this play any <video> element in a floating widow and be done with it?