In a mobile browser, the Active Games list of board positions is sized slightly wider than the phone’s display. You can tell because it’s possible to wiggle the list side to side by dragging it left and right.
This would not normally be a big problem, except that Firefox for Android doesn’t seem to handle list scrolling very well under those conditions. If you try to scroll up or down, but your finger movement involves the slightest bit of sideways motion as well, all you end up doing is wiggling the list, and no vertical scrolling happens. It’s very annoying!
My phone is a Nexus 5 running Android 6.01, and the width issue is happening in both Firefox (version 53.0.2) and Chrome (58.0.3029.83), though the consequent scrolling issue only happens with Firefox.