SELECT
   master_relation_constraints.rdb$relation_name AS reference_table
FROM
   rdb$relation_constraints detail_relation_constraints
   JOIN rdb$index_segments detail_index_segments ON detail_relation_constraints.rdb$index_name = detail_index_segments.rdb$index_name 
   JOIN rdb$ref_constraints ON detail_relation_constraints.rdb$constraint_name = rdb$ref_constraints.rdb$constraint_name 
   JOIN rdb$relation_constraints master_relation_constraints ON rdb$ref_constraints.rdb$const_name_uq = master_relation_constraints.rdb$constraint_name
WHERE
   detail_relation_constraints.rdb$constraint_type = 'FOREIGN KEY'
   AND detail_relation_constraints.rdb$relation_name = 'M_KONTRAH_GL'