If you use enlarged player that covers the whole viewport and scroll away, there's no option to perfectly focus on the player again. I wrote this simple JS, so when you middle click anywhere on the page it scrolls right where the player is (should add some functionality that allows that by default in your addon)

document.getElementById("content").addEventListener("auxclick", function(event){
if(event.button == 1)
document.getElementById("player-theater-container").scrollIntoView();
});