You can't see it in the site? In all pages except for the show classrooms one there is a certain width for the menu. The width of the MozillaWindowClass. If there is no scrollbar, the width is 1024. If there is a scrollbar the width is 1005. So 20% of a different width will give you a different width for my menu... By making the scrollbar always visible now the width will always be 1005 so the menu will always be the same width