nsPopover could be used as a simple dropdown menu. You can use the built-in ns-popover-list-theme to style the popover as a dropdown or create a custom one.

nsPopover could be used as a simple tooltip. You can use the built-in ns-popover-tooltip-theme to style the popover as a dropdown or create a custom one.

nsPopover hide when it is clicked by default, but this behavior could be changed by set the ns-popover-hide-on-click property to false. The popover above is closed only when the Close button is clicked.

nsPopover hide other popover instances when the current one is open. Can be optionally grouped.

nsPopover could be displayed at the same point the mouse is positioned, which could be used to create popver that acts as a context menu. To enabled this feature you just need to specify ns-popover-mouse-relative property to the axis to be tracked. The popover above is displayed at the same x and y position of the mouse, when clicked.

nsPopover can create a delay on the popup element.