Dorin Marcoci commited a few more fixes in PHP master branch related to Firebird PDO driver  :

Cursor is not opened on singleton selects. See the related PR #2241 .

PDO test compatibility with Firebird & Oracle select syntax. See the related PR #2244

Fix for PDO_Firebird bug #65689. PDO_Firebrid / exec() does not free allocated statement.

This leaves just a few bugs open for PDO_Firebird (some are feature requests).