Until know i hadn't any problem or incompatibility using Firebird.

Delphi 5
IBX 5.03
Firebird 1.0

Note, that 2 from the IBAdmin components (IBInstall & IBUNinstall) don't
work with firebird as they can't find interbase engine installed.
Also, in the future is possible that there will be incompatibilities between
IBX & Firebird.

Tasos Kyriakos
Athens, Greece