gistfile1.js

var f = $('yourFooterName');
var t = f.getHeight();
var y = document.viewport.getHeight();
var h = document.viewport.getScrollOffsets()[1];
if (Prototype.Browser.MobileSafari) h = window.pageYOffset;
f.setStyle({"top":parseInt(y - t + h,10).toString() + "px"});
Event.observe(window,"scroll",function(evt){
	var y = document.viewport.getHeight();
	var h = document.viewport.getScrollOffsets()[1];
	if (Prototype.Browser.MobileSafari) h = window.pageYOffset;
	f.setStyle({"top":parseInt(y - t + h,10).toString() + "px"});
});
Event.observe(document.onresize ? document : window, "resize" ,function(evt){
	var y = document.viewport.getHeight();
	var h = document.viewport.getScrollOffsets()[1];
	if (Prototype.Browser.MobileSafari) h = window.pageYOffset;
	f.setStyle({"top":parseInt(y - t + h,10).toString() + "px"});
});