@rikudou interesting, I actually have uBlock Origin *disabled* on GOG, and even disabled Privacy Badger to see if this was the issue (and reloaded after it). Despite this I see lots of warnings in console about cookies not having the correct CORS setting, so it might just be an issue with the more recent versions of Firefox being more strict in this regard. That's a good workaround to know until GOG fixes their side, though, thanks.