There is only one file type that uses the .NPFX extension:
Norton Internet Security Firewall Settings File
Settings file created by the firewall program included with Symantec Norton Internet Security for Mac; stores firewall connection blocking settings such as IP, port, service, and application filters; used for migrating firewall settings from one computer to another.
|Symantec Norton Internet Security 5||Paid|
Updated: June 12, 2013