I'm trying to do exactly the same thing as detailed in this question:
ASP.NET MVC: Redirecting back to page when no parameter is given to URL
Here's my code:
public ActionResult Details(long? id)
{
    if (!id.HasValue)
        return RedirectToAction("Index");
    Models.Track track = Models.Track.GetTrack(id.Value);
    if (track == null)
        return View("NotFound");
    else
        return View("Details", track);
}
However, when I call RedirectToAction("Index") and I'm viewing the page in Firefox 3, the page hangs.  It redirects fine in IE7.
Are there any known issues with RedirectToAction in Firefox 3?