CSS Behavior does not work in Safari or Firefox

Hi Experts,

I have a dropdown box:
<asp:dropdownlist id=cmbPeriodStartMonth CssClass="dropdown" tabIndex=-1 runat="server" EnableViewState="True" AutoPostBack="false" width="50px" style="behavior:url(Script\DateFilter.htc)"></asp:dropdownlist>

It works fine in IE but it does not work in Safari or Firefox. Is there another way to replace it?

Thank you.

<PUBLIC:ATTACH event="onchange" onevent="ProcessChange()" />
<SCRIPT language=javascript>
function ProcessChange()
{
	var ndx = this.id.lastIndexOf("_");
	var prefix = "";
	if(ndx != -1)
		prefix = this.id.substring(0,ndx+1);
	try
	{
		switch(this.id)
		{
			case prefix + "cmbPeriodStartMonth":
				MonthChange(prefix + "cmbPeriodStartMonth", prefix + "cmbPeriodStartDay", prefix + "cmbPeriodStartYear");
				break;		
				
			case prefix + "cmbPeriodStartYear":
				YearChange(prefix + "cmbPeriodStartMonth", prefix + "cmbPeriodStartDay", prefix + "cmbPeriodStartYear");
				break;
				
			case prefix + "cmbPeriodEndMonth":
				MonthChange(prefix + "cmbPeriodEndMonth", prefix + "cmbPeriodEndDay", prefix + "cmbPeriodEndYear");
				break;		
				
			case prefix + "cmbPeriodEndYear":
				YearChange(prefix + "cmbPeriodEndMonth", prefix + "cmbPeriodEndDay", prefix + "cmbPeriodEndYear");
				break;		
					
			default:
				break;	
		}
	}
	catch(e)
	{
		alert(e.message);
	}
}
</SCRIPT>

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