How to install Firehol on recent version of OpenWrt?

[Marc Lavallée]

I'm using Firehol since 2014 on an old PC,
now I want to install Firehol on a TP-Link router running OpenWrt.

Packaged versions of Firehol are available here:
https://github.com/firehol/packages/releases
The available .ipk package is for OpenWRT 19.07,
but the latest stable version of OpenWrt for my router is 21.02.3

How to package or install Firehol on a recent version of OpenWrt?

Thanks
Marc