In case of someone wanting to wrap the DLL, and create proper Xojo classes, here is the starter data to work on:
Latest API Guide available: https://www.ibphoenix.com/downloads/60ApiGuide.zip
Latest interface header: firebird/src/include/ibase.h at 69d0a38aea942960a919e9486a568a3d6549421d · FirebirdSQL/firebird · GitHub