Why doesn't AS3 FileReference Download Work in IE/FF (Works fine in Chrome)

Question

I am generating an Excel file with Java on the back-end and it seems to work just fine in Chrome but for whatever reason it doesn't in FF/IE. I have the very latest of Flash in each browser listed from this site: http://helpx.adobe.com/flash-player/kb/find-version-flash-player.html
I'm sending XML to the server, it is generating the Excel and sending it to the Flash. I'm performing the export by doing the following:
private var _fileRef:FileReference;
private function exportReport(e:MouseEvent):void
    _fileRef = new FileReference();
    _fileRef.addEventListener(Event.COMPLETE, excelExportCompleteHandler);
    _fileRef.download(new URLRequest("exportReport"), "report.xlsx");
    function excelExportCompleteHandler(e:Event):void {
        trace('complete');
There are no error messages from Java/Flash. The browse popup comes up and I save the file the same in IE/FF as I do in Chrome. the trace('complete') is executed every time in every browser but the file only shows up when using Chrome.
I also searched my filesystem and found temporary internet file shortcuts with the name of the file I was trying to download so it's as if it started the download but didn't finish it for some reason. The location of those files is AppData\Roaming\Microsoft\Windows\Recent Items

Answer 1

Definitely not a timeout, it takes < 5 seconds for the web service call to finish
I can also copy and paste the request url with data into the browser and it will successfully download the report just through the browser which made me realize I could use javascript as a non-ideal workaround solution to this problem.
I would still love to know why it was failing and if anyone has any ideas that would be great but for anyone else with the same issue as me here is the workaround I used:
as3 code (I used URLVariables to encode the data because trying encodeURI or encodeURIComponent didn't encode ' or " which would cause errors when doing the ExternalInterface.call()
var reportData:String = getReportXML().toString();
var variables:URLVariables = new URLVariables();
variables.q = reportData;
//Substring at 2 to trim off the 'q=' portion
reportData = variables.toString().substring(2);
ExternalInterface.call("function() { return downloadExcelReport('"+reportData+"')}");
javascript code (I used a hidden form because I needed to be able to perform a POST because the xml data I was passing was too large for a GET)
<script type="text/javascript">
    function downloadExcelReport(reportData) {
        reportData = decodeURIComponent(reportData);
        window.open("about:blank", "newWindow");
        document.getElementById("reportData").value = reportData;
        document.getElementById("reportForm").submit();
</script>
<form id="reportForm" method="post" target="newWindow" action="<%=SERVER_PATH%>excelReport">
    <input type="hidden" name="solutionReportXml" id="reportData" value="">
</form>