I've accidentally discovered that on some websites you can put the video to fullscreen mode using the players functionality, then use
$mod+f (fullscreen toggle), which will show the normal browser window, but the video still maximized to the window.
Next you can make the window floating and resize it.. this results in a floating video frame in front of any other non-floating window.
But that doesn't seem to work for every web video, for instance YouTube refuses to cooperate. It will simply exit fullscreen mode upon pressing
$mod+f (fullscreen toggle).
How do I reproduce this behaviour for other sites, e.g. YouTube?
To clarify what I mean, I've attached a screenshot: