postinst is in firmware-tools-cli 2.1.14-0ubuntu2.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 | #!/bin/bash
if [ "$1" == "triggered" ]; then
    for t in $2; do	
	if [ "$t" == "firmware-tools-update-firmware" ]; then
	    /usr/sbin/update_firmware --rpm -y
	fi
    done
fi
 |