Download Actions

In MAC OS I set the *default* to open pdf as Acrobat 7. 
When Firefox
asks which app to open a PDF, Apple Preview is the only one
listed and
it is shown as the default.  How do I get this to match up?

In addition, when I set Firefox / Preferences / Download
Actions, PDF
are not listed filetypes in the Change Actions Dialog box. 
How do I
**add** extensions that I want to apply actions to?  This
dialog box
doesn't seem useful unless I can add file extensions, or at
least if
Firefox listed all of the extensions that have ever been
opened.