IBSurgeon FirstAID is the tool that can automatically diagnose and repair corrupted InterBase or Firebird databases - it can repair corruptions that neither gbak nor gfix can handle.
It uses its own layer for low-level database access without using the InterBase or Firebird engine, so it can perform real "surgical" operations and repair your database when all other standard mechanisms cannot.
Now you are in 5 minutes from the recovery of your corrupted Firebird or InterBase database: