Minor problems & potential enhancements related to menu buttons & windows

[Tom Chen]

• Menu buttons should be clickable with middle and right mouse buttons.
• Click a menu button, it shows a preference window, click the same menu button, it should close the window, not close and quickly show it again.
• When a preference window is open, Esc is supposed to close the window, but in fullscreen mode, Esc will exit the fullscreen mode and not close the window.
• Menu buttons shouldn't have context menu