Alternatively, to leave the ads where they are, click the 'Compatability View' button on your web browser. It's on the left of the 'refresh' button (two arrows) at the top of your browser, on the right of the Website address bar. Clicking this you'll see it come and go. Leave it in whichever setting your happiest with and if you ever notice any websites displaying strangely, if you click it the chances are the layout problem will sort itself out.
Mine displays like yours when I'm IN compatability mode, but displays normally when I'm out of it (standard). It probably switched itself between the two somehow, which is why you all of a sudden had a problem ;-)