Firebird Blog | Firebird startup in OS X 10.11 (El Capitan)
After upgrading to OX X 10.11 "El Capitan", attempting to connect to Firebird - which had always started on boot - failed with the message:
Statement failed, SQLSTATE = 08006 Unable to complete network request to host "localhost". -Failed to establish a connection.
This is evidently to do with OS X StartupItems being deprecated for starting daemons; this blog provides a solution.