Firebird 2.5.2 Update 1 for all Ubuntu releases is uploaded into Firebird stable ppa
Here you can find the latest stable release Firebird 2.5.2 Update 1 for all supported Ubuntu releases.
Follow the Firebird 2.5.x guide for usage and installation.
What is changed is added the security fixes plus many fixes from Debian unstable repository.
Compared with previous upload support for hardy and oneiric is dropped (unsupported by Canonical)