Official announcement and release notes:
http://www.seamonkey-project.org/news#2015-03-10
http://www.seamonkey-project.org/news#2015-03-23- http://www.seamonkey-project.org/releases/seamonkey2.33/
- http://www.seamonkey-project.org/releases/seamonkey2.33#new
There is no longer a dedicated page for the changes made for each milestone. Instead, the release notes contain bugzilla links for both SeaMonkey and code shared with Thunderbird.
SeaMonkey 2.33 fixes 14 vulnerabilities, 3 of which were critical.
SeaMonkey 2.33.1 fixes 2 more vulnerabilities, both critical.