movie/video files that open your browser

Anybody know any tricks (not including Bitzi lookup) for weeding out those infuriating movie or video files that cause your web browser to open when you try to run them? That is to say, a way to recognize or avoid them in the search process, before even starting to dl them?

Or maybe there's a way to defeat the browser-opening capability of those files or the applications involved?

Seems like the culprits are usually Windows Media files and also .mov files, but some of those are good so filtering out all of them is undesirable.

I guess I could preview everything during dl, but cleaning up all the resulting preview files is a pain. Speaking of which, how come some preview files appear in the library window's list of Incomplete files and some don't?