Egg, have you tried - [youtube ]QmwrLmZDzdY[ /youtube] without the spaces?
YouTube advises Full Screen may not be possible other than through their site.
[ythd ]QmwrLmZDzdY[ /ythd] also works:
You can almost achieve Full Screen by clicking the PiP icon and dragging the top left corner up and left.
Acorn
Bookmarks