You need rAF

[danyj]

You need

requestAnimationFrame

there , script is killing your page

see this https://gist.github.com/paulirish/1579671

add raf and do this instead

$(window).bind('scroll',function(e){
  requestAnimationFrame ( parallaxImgScroll );
});

and in css

.parallax-img-container img{
    -webkit-transform: translateZ(0);
    -webkit-transform: translate3d(0, 0, 0);
    -webkit-transform-style: preserve-3d;
    -webkit-perspective: 1000;
    -webkit-backface-visibility:hidden; 
}

than you will be able to get 60 FPS

[danyj]

And if you do translate3d instead positions move, your script will be much faster and animations smoother

[cyntss]

very good tip !!! will do this as soon as i have time to check this script again :D really appreciate it!