So, I just got this when trying to post a comment on this article:
I'm assuming it's related to this update but if it's something else, sorry for posting in the wrong place!
Oh, almost forgot. I also tried disabling tracking protection, ad-blocking, and all userscripts/styles, and still the same problem. I'm using Firefox 64 on Windows.
I see this bug, too - not sure what's causing it, but I'll get it sorted out...