In many cases the drop-down menus in the menu bar to disappear and can only view the outline of the window

First, make sure the browser is not in "full screen" mode. You can switch between full screen and normal display by pressing the F11 key. Second, do you have the orange Firefox button? You can switch between the orange Firefox button and the classic menu bar; you can't have both at the same time. To change to the menu, tap the Alt key (or press F10) and then use View menu > Toolbars > ''check'' Menu Bar Does that fix it?