I created and installed a desktop java application; let's say that it's called xyzapp.exe. I also associated it in the OS with the custom file extension .xyzapp. I configure Firefox to always open (rather than download) .xyzapp files with my xyzapp application. This worked fine until about three months ago. Now .xyzapp files always download rather than open. If I tell Firefox to open .xyzapp files with Notepad, they open in Notepad. Is the latest version of Firefox unable to launch privately-developed apps. Or perhaps there is some other Firefox option that I need to set. Because my app users are complaining, I would love to solve this problem.