How to use Firebird with COBOL?
It can be done via ODBC interface. Some versions of Cobol like RM/Cobol and Acucobol provide means for that.
Additionally, Stephen Boyd gave us a tip that RM/Cobol users can also use embedded SQL via GPRE and that it would also be fairly trivial to extend GPRE to support other Cobol dialects if there was a demand for it.
You can find the Embedded SQL Guide for Firebird and RM/Cobol at:
http://www.lnssoftware.ca/firebird.htm
GPRE also claims to support ANSI Cobol and VMS Cobol, although some users have found the ANSI variant to be a bit buggy.
In case lnssoftware website is offline, you can download a backup copy of Embedded SQL Guide from FirebirdFAQ.org:
http://www.firebirdfaq.org/files/esqlcobol.pdf