Here is Part 2 again with a few modifications

In Firefox
"Edit"
"Preferences"
In the Toolbar "Applications"
In Applications there are two columns. On the Left is "Content Type" and on
the Right is "Action"
In the "Content Type" scroll down until you see "PDF document" and
it
on the down-arrow
In the "Action" column associated with "PDF document" in the "Content Type"
column on the down-arrow (mine says "Always ask")
Pick your poison. If you choose "Use Document Viewer (default)" this is the
viewer set-up in Step 1.