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

The query string works perfectly, but I wouldn’t use DateTime.Now, because it forces the user to re-download the app every time. Instead, we use the following:

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

This way all you have to do is increment the version number in the AssemblyInfo.cs file.