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

Available for Mac OS on Steam, but not here on GoG.

Devs, when are you bringing over the mac version here to GOG?
Argh, this is annoying, as I want that one too. I really don't wanna buy it on Steam.
If only gog were to advocate for it's customers. It's better to just contact devs yourself and ask them to since gog doesn't pay attention to its forums.