Although there is not yet a Firebird platform it is generally very easy to
extend support to different databases. I recommend taking a look at the
current platforms (specifically PostgreSQLPlatform or Oracle ) and see
what modifications you can make to create a Firebird platform. Then open
a bug and contribute it back. Generally only keywords need to translated
to the new platform.
If you were to switch to table sequencing you may find that
DatabasePlatform does provide you with all you need.
--Gordon