tfm-fullscreen.user.js

// ==UserScript==
// @name        Transformice fullscreen
// @namespace   https://github.com/Farow/userscripts
// @description Fullscreen mode for transformice
// @include     http://transformice.com/
// @include     http://www.transformice.com/
// @version     1
// @grant       none
// ==/UserScript==

let hide_scrollbar = 0;

try {
	init();
}
catch (error) {
	console.log(error);
}

function init() {
	let object = document.getElementById('swf1');

	if (!object) {
		return;
	}

	if (hide_scrollbar) {
		document.body.style.setProperty('overflow', 'hidden');
	}

	document.body.style.setProperty('margin-top', set_height(object) + 'px');

	object.style.setProperty('position', 'absolute');
	object.style.setProperty('top', '0');
	object.style.setProperty('left', '0');
	object.style.setProperty('z-index', '-1');

	object.parentElement.style.setProperty('height', '0');
	object.parentElement.parentElement.style.setProperty('height', '0');

	let separator = object.parentElement.parentElement.nextElementSibling;
	separator.parentElement.removeChild(separator);

	set_height(object);
	window.addEventListener('resize', set_height.bind(undefined, object));
}

function set_height(object) {
	document.body.style.setProperty('margin-top', window.innerHeight + 'px');
	object.setAttribute('height', calc_height() + 'px');
}

function calc_height() {
	let window_height = window.innerHeight,
		swf_height    = 600
	;

	if (window_height < swf_height) {
		return swf_height;
	}

	console.log(window_height + (window_height - swf_height));

	return window_height + (window_height - swf_height);
}