How do you force Firefox to not cache or re-download a Silverlight XAP file?

protected void Page_Load(object sender, EventArgs e)
{
    var versionNumber = Assembly.GetExecutingAssembly().GetName().Version.ToString();
    this.myApp.Source += "?" + versionNumber;
}

<param name="source" value="ClientBin/App.xap?<%= DateTime.Now.Ticks %>" />

Cache-control: no-cache
Pragma: no-cache

<?php $fdate = date("dHis",filemtime("MyApp.xap")) ?>

<param name="source" value="MyApp.xap?=<?php echo $fdate ?>"/>

var appTimestamp = '<%= System.IO.File.GetLastWriteTime(Server.MapPath("ClientBin/MyApp.xap")) %>';
var source = 'ClientBin/MyApp.xap?appTimestamp=' + appTimestamp;

<param name="source" value="ClientBin/App.xap?<%= System.IO.File.GetLastWriteTime(Server.MapPath("ClientBin/App.xap")).ToString().GetHashCode()%>" />

<object id="Xaml1" data="data:application/x-silverlight-2," type="application/x-silverlight-2"
width="100%" height="100%">
<%––<param name="source" value="ClientBin/SilverlightApp.xap"/>––%>
<%
string orgSourceValue = @"ClientBin/SilverlightApp.xap";
string param;
if (System.Diagnostics.Debugger.IsAttached)
param = "<param name="source" value="" + orgSourceValue + "" />";
else
{
string xappath = HttpContext.Current.Server.MapPath(@"") + @"" + orgSourceValue;
DateTime xapCreationDate = System.IO.File.GetLastWriteTime(xappath);
param = "<param name="source" value="" + orgSourceValue + "?ignore="
+ xapCreationDate.ToString() + "" />";
}
Response.Write(param);
%>
<param name="onError" value="onSilverlightError"

<%
    const string sourceValue = @"ClientBin/MyXapFile.xap";
    string param;

    if(System.Diagnostics.Debugger.IsAttached)
        param = "<param name="source" value="" + sourceValue + "" />";
    else
    {
        var xappath = HttpContext.Current.Server.MapPath(@"") + @"" + sourceValue;
        var xapCreationDate = System.IO.File.GetLastWriteTime(xappath);

        param = "<param name="source" value="" + sourceValue + "?ignore="
        + xapCreationDate + "" />";
    }
    Response.Write(param);
%>

<param name="source" value="ClientBin/MyXapFile.xap" />

<param name="source" value="app.xap?r12345"/>