> I was looking for the information on what supported transaction
> isolation mode by Firebird 1.0.3 and any changes for 1.5 RC7?

Firebird supports three isolation modes that are mapped to
corresponding JDBC isolation levels:

isc_tpb_read_committed - TRANSACTION_READ_COMMITTED
isc_tpb_concurrency - TRANSACTION_REPEATABLE_READ
isc_tpb_consistency - TRANSACTION_SERIALIZABLE

More information on native Firebird isolation levels you can find in
InterBase API documentation. Also ask in Firebird-Support group, you
should get more information there.

Best regards,
Roman Rokytskyy