Official announcement and release notes:
- http://www.seamonkey-project.org/news#2015-09-26
- http://www.seamonkey-project.org/releases/seamonkey2.38/
- The list of known vulnerabilities hasn't been updated for SeaMonkey 2.38 yet. For reference, the Firefox 41 release lists 19 fixed security issues, 4 of which were critical.
Known Issue:
The server certificate has expired and needed to be replaced. Consequently, if you update from 2.33.1 or earlier with the built-in "Check for Updates" function, you may receive a message stating "Something is trying to trick SeaMonkey into accepting an insecure update." Note that this is not an indication that your system or the server has been compromised; rather, download the full installer from http://www.seamonkey-project.org/ which will also contain the new certificate for future updates.