For me highest priority are grouping sets and pivot.

If we are talking about triggers/procedures. 

For me there is one big disadvantage about string processing.

Why we can not use indexed access to string? This should be simplified.

E.g.

 declare variable A char(50)

....

A[4] = 'x'

A[7] = A[8]

....

I wait personally for FB4 greate features like

- lateral join availability

- 63 identifiers

- big numerics

But as summary. Firebird is really strong. I really like FB stored procedures and triggers. I like transaction processing and its options. FB3 have good possibility to extend funtionality by udr.

We can create psql functions.

Regards,