It's very easy to copy existing database tables into your Firebird database. Just point Full Convert to your source database, select your target and let it copy things over.
Tutorials showing how to copy data from another database into Firebird:
It may make sense to migrate your data away from Firebird. You may want to do it permanently or just need to share your tables with a collague in a different format.
Tutorials showing how to copy data from Firebird to another database: