quote of the day from php source code

 /**
 * These aliases are provided in order to maintain forward compatibility. As Firebird
 * and InterBase are developed independently, functionality might be different between
 * the two branches in future versions.
 * Firebird users should use the aliases, so future InterBase-specific changes will
 * not affect their code
 */

you can browse firebird extension on php.net

.:(firebird):..:(databases):..:(sql):.