When you right-click on a window thumbnail, a menu should appear, but instead the window thumbnail just disappears. The screenshots show 1) a Firefox mini-window 2) a mini-window that just disappeared when you right-click 3) a mini-window of any other program 4) the menu that appeared is as it should be Otherwise the browser works absolutely fine for a long time. But this problem causes a lot of inconvenience because I have 2 monitors.