//bottom

if (window.innerWidth) { //if browser supports window.innerWidth (mozilla)
     theTop = window.innerHeight-50;
     //alert('mozilla')
}
else if (document.all) { //else if browser supports document.all (IE 4+)
     //alert('windows');
     theTop = document.documentElement.clientHeight-50;
     
}
else if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) {
//IE 4 compatible
    theTop = document.body.clientHeight-50;
}
//alert(theTop);
var old = theTop;
var pos = 0;

init_top();