I have a couple of thoughts. Try this: select one of the files that you've downloaded, Get Info, then change Open with to Quicktime Player and underneath, Change all. I can't promise but it may help. Also, what browser are you using? You should be able to tell it not to open the file. In Firefox, for example, it's under Prefs>Content>File Types and then you can just have it safe the files rather than open them. I think, in Safari, Preferences>General and then uncheck Open safe files after downloading.