Hi kenkahn, a little while back, Firefox started using a file named '''handlers.json''' to store customized application handler settings. There also was a change in what is stored in the file; based on what I see, it does not record your system's default email program. Screenshot #1 shows the two built-in handlers (Gmail and Yahoo Mail) along with MS Outlook, my default application, on the Options page. If you do not have the default handlers, your handlers.json file may have become damaged. Screenshot #2 shows the data from handlers.json (in a Firefox tab). Whether I set Outlook as default or not, Firefox doesn't add Outlook to the file, it just changes one or two parameters. ''It's all a bit mysterious...''