When looking through the tutorial, you come across an image that you want a closer look at. You click it, expecting it to either navigate to the page or popup. Instead, it appears that a modal grey screen appeared over the page.
What's happening is that the image is opening in the middle of the HTML page, not the middle of the browser window. So if you are on page 1 of 10, you have to scroll down 5 pages to see the image. Once you dismiss it, you then have to scroll back up 5 pages and find where you were reading.
It would be ideal if it would open in the context of the current window dimensions rather than the generated html page dimensions.