<mx:ComboBox
    xmlns:fx="http://ns.adobe.com/mxml/2009"
    xmlns:mx="library://ns.adobe.com/flex/mx"
    xmlns:s="library://ns.adobe.com/flex/spark"
    selectedIndex="1"
    width="150"
    layoutDirection="rtl"
    direction="rtl" open="cb_openHandler(event)" >
    <fx:Script>
        <![CDATA[
            import mx.events.DropdownEvent;

            protected function cb_openHandler(event:DropdownEvent):void
            {
                this.dropdown.height = 150;
            }

        ]]>
    </fx:Script>
    <mx:dataProvider>
    	<mx:ArrayCollection>
    		<fx:String>Product A</fx:String>
    		<fx:String>Product B</fx:String>
    		<fx:String>Product C</fx:String>
    		<fx:String>Product D</fx:String>
    		<fx:String>Product E</fx:String>
			<fx:String>Product F</fx:String>
		</mx:ArrayCollection>
	</mx:dataProvider>

</mx:ComboBox>