I'm on an Android Motorola X 2nd Gen., running Android 5.1. I get the "This plugin is not supported." box, but right directly below it is another box with the Youtube video, which runs fine. I'm not sure if I had to touch the "not supported" box first in order to get the second Youtube box, but whether I did or didn't, it seems pretty intuitive to me, and I'm *very* computer-stupid.
I guess I'm fine with it.