<<For configuration issues such as the one you described, you may want to purchase a copy ofthe Firebird Migration Guide at the link below...
https://www.firebirdnews.org/migration-guide-to-firebird-3/
Though it is titled as a migration guide it covers a lot more than just moving databases from Firebird 2.5 to 3.x.>>

Or ifyou are seriously interested in Firebird
http://www.ibphoenix.com/products/books/firebird_book

Paul