1. Launch up Script Editor (Applications > AppleScript > Script Editor)
2. Select New from the File menu to create a new empty script
   
3. Copy the code listed below in-between the "--Start" and "--End" comments
4. Paste this code into the blank empty script in Script Editor
5. Save the script in your ~/Library/Address Book Plug-Ins/ directory and name it "Google Map Of.scpt"
   
6. If the Address Book application is open, quit it
7. Launch Address Book and select someone with a U.S. address
   
8. Right-click or control-click on an address and select 'Google Map Of (Firefox)' from the pop-up menu
9. FireFox should open up with a map
10. Enjoy
    

-- Start
property googleMaps : "http://maps.google.com/maps?q="

using terms from application "Address Book"

on action property
return "address"
end action property

on action title for p with v
return "Google Map Of (Firefox)"
end action title

on should enable action for p with v
return true
end should enable action

on perform action for p with v
set params to ""
if street of v is not missing value then set params to params & street of v & " "
if city of v is not missing value then set params to params & city of v & " "
if state of v is not missing value then set params to params & state of v & " "
if zip of v is not missing value then set params to params & zip of v & " "
try
tell application "Firefox"
OpenURL googleMaps & params
activate
end tell
on error
display dialog "You must have Firefox installed to use this plug-in."
end try
end perform action

end using terms from
-- End