That's the initial page that clicking on the submitted link redirects to. The back button seems to work in a standard way for navigation with the webpage itself (as it's just a single html file; it's Tiddlywiki after all); it seems that the back button is broken only across the initial navigation from an external site to this webpage. That's ok with me personally (just have to long press/long click the back button on Chrome/Firefox, and on Safari even the initial navigation works fine), given everything else that this page is doing. (Besides, in practice if you were to use this you would be opening the downloaded index.html file in a separate tab/window anyway, not navigating to it from other webpages.)