I'm experiencing unusual behaviour today, Tues Dec 11/18 about noon EST. Whenever I click on a thread to read it, your system lodges TWO links in the "back-arrow" key at upper left. So when I hit that arrow it returns to the same thread I'm already reading and then I have to hit the back-arrow a second time to return to the Forum category I started from. This does not happen with other websites in other browser tabs, so I don't think it is my Firefox misbehaving.