There is only one file type that uses the .NFB extension:
Nokia Phone Backup File
Backup file created by Nokia PC Suite, an mobile phone management application that synchronizes Nokia mobile phones with a PC; contains a backup of the phone's data, including user and system data; used for restoring phone data to the same phone or transferring data to another phone.
NFB files are created using the Nokia Content Copier program within the Nokia PC Suite. Nokia Content Copier is sometimes also called Nokia PC Suite's "Backup and Restore" utility.
NOTE: Nokia phone backup files also use the .NBU and .NFC extensions.
Updated: May 23, 2011