Finally figured it out; and since earlier posts raised the issue but didn't have this solution, I decided to post what worked for me. 1. Download an example of the file type you're having issues with 2. CTL-J or click the down-pointing arrow icon ("display the progress of ongoing downloads") at top right of menu bar 3. Right-click the file name of the item you just downloaded; then choose "Always open similar files" Adding the file type to Settings > Applications was not an option. Windows Media Pack was a red herring. Autoplay is a different thing. Hope this helps someone, or maybe ME the next time I forget.