since some versions media (movies, mp3, what ever is recognized) start automatically in the viewer pane. I have disabled (also enabled and disabled it again) the option "Automatically play Movies" in the Movie plugin and applied the hint from an older post, but still the media files start to play on selection.
Configure the ActiveX plugin and within there turn on the Windows Media Player line in the top part of the list (Preview Handlers). That should not autoplay (unlike WMP itself; the preview handler is different).