when the page is smaller than scrollbar size, scrollbar disappears though the page is scrollable. As you see the attachment, Chrome's scrollbar changes its look when the area is getting smaller than the bar's size, but Firefox's just disappeard. seems have new line or failed to be rendered. tested in: https://nhnent.github.io/tui.calendar/latest/tutorial-example01-basic.html change the height of rows in table to have enough space for scrollbar and to have not enough space for scrollbar. the reason why this may be critical is that it changes total width of element. so the table looks broken.