Just use left property instead of margin-left to set the image at the right place. Different browsers will be left to guess differenty for position fixed element.So the bext pactice will be to include left and top properties for your element
span.boy_hand {
background:url(../img/hand_png.png) no-repeat;
height:35px;
width:51px;
position:fixed;
top:470px;
left:32px; /* Set left property as per your need,I just simple reused your code */
}