It seems that Sun is working on a database to be released with their own brand:

http://jroller.com/page/thinksInCode/20050205#sun_open_source_database_what

There also is a poll about what will Sun DB be based on and Firebird is one choices:
http://www.manageability.org/polls/sun-db

I personally think (if all this news are true) that it will be based on the same engine used by OpenOffice.org 2.0.

Marcello