Hi,
Install this bookmarklet:
javascript:(function(){
var body=document.getElementsByTagName("body")[0];
var head=document.getElementsByTagName("head")[0];
var html=document.getElementsByTagName("html")[0];
var game=document.getElementById("game");
html.insertBefore(game.parentNode.removeChild(game),head);
html.removeChild(head);
html.removeChild(body);
var s=html.style;s.height="110%";
window.scroll(0,35);
})();
And run it over at runescape.com
It moves the game to the root <html> tag and then deletes everything else (remove <head> and <body>).
It also resizes the <html> tag to fill 110% of the height of your browser window to enable scrolling. Then it scrolls down 35 pixels to position the game just right. (Get rid of as much of game bar as possible.) You can then go full screen with F11 (That's what most browsers use by default.)
Works best if you lower your screen resolution to 800x600.
Enjoy,
--3ICE