The common factor in both cases seems to be that Robert has posted a link to another post on the forum in a ‘clever’ format that shows part of the text of the post and allows you to expand it to see the whole post. The problem occurs if you middle-click on the thread title of the link, to open the thread in another tab. Then the link tries to open a popup for some reason and Firefox activates its popup blocker and stops it.
Code that intercepts my mouse clicks and changes them to cause popups is very badly behaved IMHO.
That format was automatically applied by Discourse (the forum software). I did nothing special. I can suggest two courses of action: whitelist openenergymonitor.org in your pop-up blocker, or ask on the Discourse forum.
I use Opera browser and I have pop-ups blocked, but see nothing unusual. The linked thread opens in the same window for me.