What ADO drivers (not .Net) exist for Firebird?
Take a look at one of these websites:
there is an example how to use it with Visual Basic:
Update: website praktik.km.ua is no longer available, but you might have luck looking at the snapshots in Internet Archive. For example, this one from year 2008:
If you wish to use Firebird with Visual Basic, you might also want to take a look at this:
It's a stand-alone DLL library without any dependencies.