<img id="test" src="pump.gif" width=116 height=123 style="-moz-opacity:0.3" />

<script type="text/javascript">

opacity=0 //opacity of image
var increase=1 //increase opacity indicator
var decrease=0 //decrease opacity indicator

function fade(){
if (opacity<0.6&&increase)
opacity+=0.05
else{
increase=0
decrease=1
}

if (opacity>0.3&&decrease)
opacity-=0.05
else{
increase=1
decrease=0
}

document.getElementById("test").style.MozOpacity=opacity
}

if (document.getElementById("test") && document.getElementById("test").style.MozOpacity) //if Firefox/ NS6+
setInterval("fade()",100)
</script>