[in reply to SunshineMeadows, message #60]
Thank you for working on this issue some more.
No problem. I was afraid that trying to use the workaround for more than one file type might throw up errors, which is why I was hoping to find a more general solution. Unfortunately, I've exhausted all the options I can think of, so I've pretty much given up on it for now. If I happen to come across a solution in future, I'll let you know.
On a related note, I can now tell you that hand-editing Firefox configuration files to see what happens is not a good idea. Don't do this at home, kids, I'm a trained professional (: