> One interesting thing is, i have never faced this kind of issue in
> MySQL. The problem is with Firebird only.

Did you use transactions with MySQL? What isolation level do you use for
Firebird?

> Wont the Firebird engine lock the row before updation?

No. Firebird has completely different scheme - it allows two concurrent
transactions to update the same row without lock conflict, conflict will be
reported only on commit.

> Will he allow other thread also to access the same row for updation?

The issue is not related to another thread, but to the way you manage your
transactions.

If two concurrent transactions modify the same row, one of them must be
rolled back in order to preserve the database consistency. If you don't
really care about the data consistency - use auto-commit mode - each update
will be committed.

Roman