Cannot start Support-Chat from my hub

Hi,
when I start a support-chat window, I will be prompted to "enable cookies", although I have never disallowed them!
"Cookies are not enabled in your browser. Please enable cookies before starting a chat." is always presented in chat-window.
My AdBlocker "Privacy Badger" is disabled for premium.wpmudev.org.
It worked well before …
Any idea what to do?
Mac 10.13.3, Firefox latest 59 …
Thank you and kind regards,
Sascha