I have Firefox set to ask me first whether I want to open or save a file that I select. After disabling full-page plugins for midi files, I found that Firefox would allow me to navigate anywhere in the file system to find a helper app to play a midi file (but does not seem to remember it). Why does it not treat .pdf files the same way? Going thru the same rigmarole with midi files as for .pdf files to get the app of my choice does not change the behaviour.