Incompatibility between unixODBC and Firebird ODBC driver
I came to a solution, if anyone is interested:

For any reason, firebird ODBC 64-bits driver downloaded from oficial site comes with SQLLEN = 4 bytes. After some help, I managed to compile driver from source code, and the result seems to work with 8 bytes SQLLEN.

In the compile proccess, I had a BUILD_DRIVER_VERSION error, modifying line 139 (SetupAttributes.h), adding spaces between each number fixed it.