test.htm
<style>
span {-moz-binding: url(test.xml#custom);behavior:url(test.htc);cursor:pointer;background:#ddd;}
</style>
<span> test </span>
//IE
test.htc
<attach event="onmouseup" onevent="up()"/>
<attach event="onmousedown" onevent="down()"/>
<script language="javascript">
var currX = 0;
function up(){
alert(currX);
}
function down(){
currX += 1;
}
</script>
//Firefox
test.xml
<?xml version="1.0"?>
<bindings xmlns="http://www.mozilla.org/xbl" xmlns:html="http://www.w3.org/1999/xhtml">
<binding id="custom" styleexplicitcontent="true">
<implementation>
<property name="currX">0</property>
</implementation>
<handlers>
<handler event="mousedown">
this.currX = event.clientX+this.currX;
</handler>
<handler event="mouseup">
alert(parseInt(this.currX));
</handler>
</handlers>
</binding>
</bindings>