Code:

 

<script type="text/javascript">
//created by Holysavior of ZBCode and Javascriptin.com

if(location.href.match(/\/post\//i) ){
$("#c_bbcode").append("<button type='button' id='flash' onclick='workflash()'>Flash</button>")
$("#flash").insertBefore("#c_bbcode select");

function workflash() {
var height = prompt("Height of the File?");
var width = prompt("Width of the File?");
var url = prompt("URL of the File?");

document.forms['posting'].post.value="[flash="+width+","+height+"]"+url+"[/flash]"
}
}
</script>