Philippe Makowski announced :

Firebird 2.5 rpms are in Fedora rawhide (Fedora 15), on EPEL6 beta for

RHEL6 and future Centos6

https://admin.fedoraproject.org/pkgdb/acls/name/firebird

For Fedora 14 (the actual stable Fedora) I made a private repository here : http://repos.fedorapeople.org/repos/makowski/firebird/