How to remove titlebar when maximising youtube videos in awesome 3.5?

How to remove titlebar when maximising youtube videos in awesome 3.5?

Since I migrated from awesome 3.4 to 3.5 I am unable to remove titlebar
from youtube videos when maximising fullscreen.
In awesome 3.4 I used to put:
{ rule = { instance = "plugin-container" },
properties = { floating = true } },
and that works. However in version 3.5 the titlebar "plugin-container"
remains. I even tried the following without much success:
{ rule = { instance = "plugin-container" },
properties = { floating = true } ,
callback = function (c) awful.titlebar(c, {size = 0}) end },
However the function works when I hooked it to a keybinding:
awful.key({ modkey, }, "w",
function (c) awful.titlebar(c, {size = 0}) end
I know for sure that the rule works because it makes the window floating
but does not execute the call to the function, so I am really perplexed to
what is the issue here.
Thank you,