Have tested this on a variety of video players, including YouTube, CBC Gem, PeerTube and others.
1) Open video player, play video
2) Switch to another tab
3) Switch back to video tab
4) Attempt to use keyboard shortcuts to start/stop (space), mute (m), forward/back (arrow keys)
They do not respond unless you click into the tab/video window first. Before the .9rc, this would work as expected and not require you to click anything first.