I've attached a screen shot. I tried different youtube videos. I also tried ie7 instead of FF3. It seems to download, get to 100%, pause, then give the javascript error and never sends me to the ringtone editor page.
Hope this helps. I noticed this behavior first on saturday july 11th...
It appears to just be effecting youtube downloads. If I use the upload a file from your PC option that works. (if that helps narrow things down at all)