1. I did write what browser is use.
2. It's the case for a few weeks now, so it's either an actual "upgrade" of firefox or an change in wordpress. I would rather guess second.
3. The suggestion to deactivate all security (addons) isn't one to follow.
4. At the page third party cookies are not the cookies necessary named, so I can allow the pages.
5. Also which sites need Java Script isn't mentioned.
(I see gravatar.com, kissmetrics.com, optimizely.com, cloudfront.net, googleapis.com, gstatic.com)
6. Since I didn't changed anything about this it is a change from wordpress site, if cookies or Java Script are the troubleshooter.