We were talking about what was the best browser… and now Firefox gives me this surprise.
If you don’t enable to accept cookies, it will not use the exception list to allow some sites.
So you have to select to use cookies. But the new 60 developer version does this correctly.
It’s a sad bug on version 59, but it’s not this that will make me give up on Firefox.

I was testing putting a list of selected websites on the exception list to allow them and only them to use cookies.

It’s not an Antergos/Arch problem, I just wanted to report this here so we know about it.