Network Security Services (NSS) is a set of libraries designed to support
cross-platform development of security-enabled client and server applications.
Applications built with NSS can support SSL v2 and v3, TLS, PKCS #5, PKCS #7,
PKCS #11, PKCS #12, S/MIME, X.509 v3 certificates, and other security standards.

If you don't care for seamonkey as a browser and are concerned about the vast
amount of space it consumes on your hard drive, you can install mozilla-nss
instead of seamonkey. Typically one of the two has to be installed if you want
to build a package that depends on nspr (the netscape portable runtime
libraries) and nss.