addEventListener on youtube API with greasemonkey - youtube

Question

I would like to use Greasemonkey to access some API objects of youtube videos while I'm in fullscreen mode.
It could be useful to have mouse clicks and position relative to screen.
This, to detect fullscreen mode, doesn't work:
window.fullScreen
I tried also to add mouse event detection to yt player, with this:
var player = document.getElementById('movie_player');
player.addEventListener("click", interceptClicks,true);
but it doesn't fire that func.
I tried also to inject some code like this:
function GM_main () {
var playerNode = document.getElementById ("movie_player");
playerNode.addEventListener ('click', interceptClicks ,false);
}
addJS_Node (null, null, GM_main);
function addJS_Node (text, s_URL, funcToRun, runOnLoad) {
var D = document;
var scriptNode = D.createElement ('script');
if (runOnLoad) {
scriptNode.addEventListener ("load", runOnLoad, false);
}
scriptNode.type = "text/javascript";
if (text) scriptNode.textContent = text;
if (s_URL) scriptNode.src = s_URL;
if (funcToRun) scriptNode.textContent = '(' + funcToRun.toString() + ')()';
var targ = D.getElementsByTagName ('head')[0] || D.body || D.documentElement;
targ.appendChild (scriptNode);
}
I tried also to make a:
window.addEventListener('click', interceptClicks, false);
This works, BUT only in all areas different from the youtube flash player in non-fullscreen mode and in fullscreen mode, obviously none area, as there is only the player visible...
EDIT:
I made a partial progress indeed.
I created a button element with
btn.addEventListener("click", function () { player.mozRequestFullScreen();}, false)
This way flash video enters in Firefox fullscreen mode and so it receives the wheel events fired by the
window.addEventlistener('DOMMouseScroll', .....etc)
Besides, the fullscreen mode is detected by
window.fullScreen
Also, all keys (event) are detectable, but ESC; not again the mouse clicks..
There is a drawback:
Once in fullscreen, SOMETIMES if you click the left mouse button it suddenly exits fullscreen mode... SOMETIMES instead it stays normally full...
To exit it's not sufficient to press ESC, you need to press the normal flash fullscreen button on the lower right + ESC.
Some rare times it blocks itself in Fullscreen mode and you can't exit. You should press ctrl+alt+canc and then it appears firefox "block script" dialog box.
Why that odd behaviour and how to prevent it?
Ideally the best should be: intercept mouse click on the lower right flash fullscreen button, block it, redirect the call to mozFullscreen and block the fullscreen mode until you press ESC.
But I dont' think it's possible, is it?