None (see changes page for minor changes).
Mozilla platform changes
CSS3 Animations, Transitions, Transforms and Gradients have been unprefixed.
MD5 is no longer supported as a hash algorithm in digital signatures.
The Opus codec is now support by default.
The reverse CSS3 animation direction has been implemented.
Per tab reporting is now available in about:memory.
Fixed several stability issues.
The changes page lists a more detailed overview of new features and fixes relative to our last stable release, SeaMonkey 2.12. Relevant security fixes are listed on Security Advisories for SeaMonkey.