K, Activity feed might not work correctly on older browsers. I highly advise you all updating your browsers to the latest available version. In case of FireFox, at least to 52 Extended Support Release

edit:
Easy to manage adblock replacement: uBlock Origin

Alternatively it may be you need to update your script / ad blockers settings as the activity feed seems to rely on some new domains that you might be blocking.

Win 7, Firefox 47.

Edit: I just checked your previous post and saw your edit, in that case we're both using the same browser version, haha!

I'm using uBlock Origin as well, however even when it's disabled on GOG the activity feed is permanently broken. Personally I don't really see a point in updating as uBlock seems enough, and it won't break any of the other addons I'm using. Not to mention I don't like how the new version of Firefox creates new instances of FF for each tab (see the Task Manager), like Chrome does, instead of keeping it as one like now.