For which types of files does this happen (which file extension)? If you can provide an URL to a RSS feed, I could try it.
You can access the advanced config editor by opening the preferences dialog and pressing Fullscreen-Fullscreen-Plus-Minus-Plus-Fullscreen. There you can set the "videoplayer" variable. And yes, as danramos already pointed out, this might not be the best solution. I'll think of a better way to access the advanced configuration dialog for the next version