I am guessing you can't also click the "show unread posts since last visit" and "show new replies to your posts" links?
My theory: the banner is set at 100% width and your browser doesn't support Viewport to resize it to fit to you, so the banner link sort of goes on top of the links to the right even though it doesn't look like it's on top. It is a problem with older browsers and the one I like to use, unfrotunately, but I think the newest Firefox should support it? I would suggest you to double check if you have the latest version.
Why the banner is set up this way is so that people with even smaller monitors don't have the banner go on top of the links to the right, which was a problem earlier for some. Now it should be cut off before it happens, but if your browser doesn't support Viewport, this little problem rears its ugly head.
Also waffles already asked but I wrote you this tl;dr anyways. Correct me if I'm wrong, waffles.