> > Firebird doesn't support multiple threads _concurrently_ using
> > the same connection.

So this entire discussion is moot.

Yes, for example in a GUI application, you can have multiple
datasets open, and keep them open while you save your data
by using another transaction.

That sounds pretty fishy - it's like they decided add the feature to
cater to a simplistic use of the Delphi programming model. Since "they"
are Borland, it is their right to make that decision. However, I feel
that leaving transactions open for more than the milliseconds required
to do the work is not an especially sound design practice. Apart from
the result sets kept in memory, there are risks and processing
requirements involved in handling dropped connections and abandoned
transactions.