Do you know if the website where you are downloading the files from is set up with the correct mime types? Often if the server doesn't know what the file types are, it serves them as generic xml.

An alternative solution could be to right-click the file and save it some place on your computer. Then when you double-click the file, Windows should recognize it and use the appropriate program.

For reference, here's the article we have about this - Manage file types and download actions in Firefox

I don't know if the source server sends the right mime type - it probably doesn't. In fact, now you mention it, I'm not sure I've tried this from any sites except one, which is the one giving me problems. I'll try contacting them about fixing their mime types. Assuming though that they can't or won't fix it, the question still remains - is it possible to set application by extension rather than by mime type?

Yeah, I can definitely save it and open it, just trying to take the easiest possible route for a quick view.

Thanks.