The Userguide of Codeigniter 3 (still Release Candidate) mentions that now has support for Firebird:
Added Interbase / Firebird database support via the ibase driver.
This means that the installation package CI 3 includes it, although you could previously use Firebird in CodeiIgniter 2 by the driver developed by Carlos García ( https://github.com/cgarciagl/Firebird-for-Codeigniter ) .
To see the rest of the new features of CodeIgniter 3 these are the addresses:
We can confirm that CodeIgniter 2 is a stable platform where I ‘ve done development with very good results in the past.
I also put the direction of an article I wrote about using Firebird with CodeIgniter 2, in my blog:
ps: news via firebird.com.mx