IE and Firefox Incompatabilities with Downloader Object

Question

 I have the following code which works perfectly in IE but not Firefox.  I get an Error 2207 on all the lines obtaining data from the sender object.

function LoadDigitalForm(sender, args)
{
    _control = sender;
     // Create a Downloader object.
    var downloader = _control.createObject("downloader");
    // Add DownloadProgressChanged and Completed events.
    downloader.addEventListener("downloadProgressChanged", "OnDownloadProgressChanged");
    downloader.addEventListener("completed", "OnCompleted");
    // Initialize the Downloader request.
    downloader.open("GET", "silverlight.ashx?formid=8588", true);
    // Execute the Downloader request.
    downloader.send();
}

function OnDownloadProgressChanged(sender, args)
{
}

function OnCompleted(sender, args)
{
   if(sender.status == 200)
   {
        alert(sender.getResponseText("Form.xaml")); //Firefox will bomb here
        var baseImage = sender.findName("baseImage");
        baseImage.setSource(sender, "Base Image.png"); //Firefox will bomb here
        var xamlFragment = _control.content.createFromXamlDownloader(sender, "Form.xaml"); //Firefox will bomb here
        var root = sender.findName("rootCanvas");
        root.children.add(xamlFragment);
   }
   else
   {
        alert(sender.statusText);
   }
}

Answer 1

 I have resolved this issue with firefox.  If you are streaming a ZIP file that is dynamically generated through say an HttpHandler, you must set Response.Buffer = true otherwise Firefox will bomb.  Also, use ContentType = application/x-zip-compressed.