About Firepower Licenses
Your Firepower products (Firepower Management Center and managed devices) include licenses for basic operation, but some features require separate licensing or service subscriptions, as described in this chapter.
A "right-to-use" license does not expire, but service subscriptions require periodic renewal.
The type of license your products require (Smart or Classic) depends on the software you use, not on the hardware it runs on.
"NGFW" means different things to different people, so this documentation does not use this term.