No, I am not asking how to set a default application or action.
Now that I have that out of the way, I want to know how to determine the default selected radio button for the download dialog:
I would like PDF files to have "Open With" default pre-selected, and everything else to have "Save File" pre-selected. The important thing is that I still want the download dialog to appear, but I don't like how firefox automatically selects one radio button or another (seemingly at random). Someone posted exactly what I am asking for (in much more detail) here: https://support.mozilla.org/en-US/questions/958705#answer-434781
As far as I am aware, Firefox determines what radio button select, but this cannot be changed by the user...