If use the PrivacyBadger anti-tracking extension with your browser and you have problems viewing the forums (e.g. site stays empty except for a few non-working links), click on the badger icon and set “discourse-cdn-sjc1.com/business5”, and possibly “avatars.discourse.org” to allow.
This fixes the problem.
I’m probably not the only one with a paranoid setup like this, so maybe this is helpful to someone. I have reported this as a broken site problem to the EFF so hopefully there will be an automatic solution.