Visualforce Charting with drill down when clicking on chart sections/bars

VisualforceDrilldownChart.page

<apex:chart height="300" width="300" data="{!data}”>
    <apex:axis type="Category" position="bottom" fields="ctype">
        <apex:chartLabel rotate="270"/>
    </apex:axis>
    <apex:axis type="Numeric" position="left" fields="cval"/>
    <apex:barSeries axis="left" orientation="vertical" xField="ctype" yField="cval">
        <apex:chartTips rendererFn="renderer"/>
    </apex:barSeries>
</apex:chart>

<script type="text/javascript">
function renderer(klass, item) {
    var type = item.storeItem.get('ctype');
    var val = item.storeItem.get('cval');
    var e = window.event;
    var t = e.target || e.srcElement;
    t.onclick=function(event){
        window.parent.location = "{!$Page.MyDrilldown}?type="+type;
    };
    this.setTitle(type + " : " + val);
}
</script>

@sohalloran, This code doesn't work with firefox as window.event should be injected to the function, for it work in firefox. Any pointers how to make this work in Firefox.

Thanks in advance.