Where do you see those two entries and which Firefox versions are involved? If you see them only as entries in the installed programs list then you may only see an orphaned entry that wasn't removed by the updater and both may point to the same program folder. In that case you can remove that registry key yourself or use a registry cleaner if you aren't experienced or feel comfortable with editing the registry. *HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Mozilla Firefox (????)