Official announcement and release notes:
- http://www.seamonkey-project.org/news#2014-06-16
- http://www.seamonkey-project.org/releases/seamonkey2.26.1/
What happened to 2.27?
The short story is that the Gecko 30.0 platform changes require newer system libraries, and hence updates to the builders, especially on Linux (which is still lacking nightly builds due to that reason). This hasn't happened yet.
See viewtopic.php?f=6&t=2837375 for the respective discussion in the SM Builds forum.