I did some testing and it looks as though Firefox 3 passes referrer information even if you haven't visited the page. I don't know if it works with downloading a video. But it does appear to work if someone plays the video. Time to get to work on a new method, I guess, as anything referrer related is going to be pretty much defeated. Strangely enough, IE 8 appears to do this as well (IE 8 Beta 2). So, whenever IE 8 officially releases, this may become a bigger problem.