You can find the new features and bug fixes in NSS 3.13 with this
Bugzilla query:
https://bugzilla.mozilla.org/buglist.cgi?list_id=1496878&resolution=FIXED&classification=Components&query_format=advanced&target_milestone=3.13&product=NSS
Some notable changes include:
1. SSL 2.0 is disabled by default.
2. A defense against the SSL 3.0 and TLS 1.0 CBC chosen plaintext attack
demonstrated by Rizzo and Duong (CVE-2011-3389) is enabled by default.
Set the SSL_CBC_RANDOM_IV SSL option to PR_FALSE to disable it.
3. SHA-224 is supported.
4. Ported to iOS. (Requires NSPR 4.9.)
5. Added PORT_ErrorToString and PORT_ErrorToName to return the
error message and symbolic name of an NSS error code.
6. Added NSS_GetVersion to return the NSS version string.
7. Added experimental support of RSA-PSS to the softoken only
(by Hanno Böck, http://rsapss.hboeck.de/).
Wan-Teh Chang