It seems that you're using an outdated browser. Some things may not work as they should (or don't work at all).
We suggest you upgrade newer and better browser like: Chrome, Firefox, Internet Explorer or Opera

It's a pain in the neck to install this on top of the GOG version and the developer bothered to put it on Steam, as version 1.5 I think.

Basically the mod requires an older version to work.

And the developer of the game liked the mod enough to include a switch in the official game so we don't have to downgrade.