Opening pdf files

When I click on a pdf file in Firefox 1.0PR, it always tries to open itself
in Adobe Acrobat. I would like to use Preview instead, but it isn't
selectable when I try to use the Downloads > File Types > Change Action
option in the Firefox preference pane.

How do I make Preview the default app for viewing pdf files in Firefox in
Mac OS X?

I also put the 'PDF Browser Plugin' into my Internet Plugins folder, but it
doesn't do anything. When I look Downloads > File Types > Plugins preference
pane, the entry for it shows up as PS - Postscript File - Enabled shows up.
Is that right?

Thanks

Vince