It used to be that if people included links in their posts, when you clicked on it, it opened in a new tab/window. Now it just opens in the original one, so that by the time you've looked around the linked site, it takes a great very many back-clicks to get back to the thread you are reading. It's also a pain if you're comparing several links people have included in the same thread.
(I know you can control-click and select a new tab each time, but it was much easier when it happened automatically, and I don't know why it changed or whether it was intentional).