This Discourse instance says, under Terms of Service, User Content License:
User contributions are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
This makes it at least unclear whether commercial use of the forum, such as taking part in discussions as a paid employee, is permitted at all. What’s worse, the non-commercial Creative Commons variants have a huge range of possible conflicting interpretations, and what they say in legal terms is often not what authors expect. The general Mozilla terms at least do not have this particular problem.
I was about to write that the same thing applies to Discord. But they changed their terms today and dropped the restrictions to personal, non-commercial use.