> 1. Is Firebird is good with the use of VB6? What is the best OLE DB
> provider to be used with VB6?

This is not easily answered. You should try out which driver does fit
your needs best.

I did compare OLEDB drivers years ago regarding my needs: The where all
more or less slow presumably due to that what ADO does with the OLEDB
driver.

> 2. What is the advantage and disadvantage of Firebird over
> MySQl/PostgreSQL? in terms of stability,security and performance.

Performance-comparisons are hardly possible in short. I would expect any
of these databases to have reasonable performance.

There are certainly situation where the generational storage of FB and
PG is an advantage or an disadvantage. It is an advantage if you have to
backup an active system: With generational storage you can make an
consistens backup of DB at the time of backup starting without blocking
other processes in accessing your DB.

Elmar