How to keep YouTube video fullscreen after moving mouse to other screen in Awesome WM

I have this problem as well. I think it's related to the bug herein:

http://osdir.com/ml/blfs-support/2011-12/msg00059.html

The problem seems to be related to specific functionality in gtk 3.0, likely related to resizing the window or making the resize grip appear: I've gotten this behavior when I use Meta-Mouse2 to resize in Awesome. I've also seen it happening just in the course of regular use. Some things that might help:

1) You can begin closing random gtk windows. In my experience, the problem only reliably goes away when I close my last gnome terminal. I should really find a non-gtk terminal that pleases me.

2) Always run awesome with your windows in some layout rather than free. This will make the resize grip not show up accidentally.

Other than that, I think the best you can do is wait for someone to figure out the code path and fix this problem.

It's a bit tricky:

You're right "plugin-container" looks quite like firefox.

Unfortunately you cannot distinguish the newly spawned yt-client by "instance" since it's simply an empty string, which matches more clients than you want.

I have found another way: The "class" property of that client is "Luakit" instead of "luakit" for normal luakit-clients. So a corresponding rule could look like this:

{ rule = { class = "Luakit" },
   properties = { floating = true } },

But that distinction seems likely to be changed in the future.

You could find out more about the properties of the clients by adding the following code to your rc.lua

mytimer=timer{timeout=2}
mytimer:add_signal("timeout",
        function () for i,c in ipairs(client.get(mouse.screen)) do
                        if c:tags()[mouse.screen]== awful.tag.selected(mouse.screen) then
                                naughty.notify({title=c.class,text=c.role})
                                naughty.notify({title=c.class,text=c.instance})
                                end
                    end
        end)
mytimer:start()