The contextmenu event is fired when the right button of the mouse is clicked (before the context menu is displayed), or when the context menu key is pressed (in which case the context menu is displayed at the bottom left of the focused element, unless the element is a tree, in which case the context menu is displayed at the bottom left of the current row).
In Gecko this event is handled by a XUL ancestor element, even for HTML5 context menus, which are actually handled by the browser element's context menu. If a XUL ancestor element has a context or contextmenu attribute referencing a popup, then display it (subject to the popupshowing event).
For mouseover, mouseout, mouseenter and mouseleave events: the target of the complementary event (the mouseleave target in the case of a mouseenter event). null otherwise.
The X coordinate of the mouse pointer in global (screen) coordinates.
The Y coordinate of the mouse pointer in global (screen) coordinates.
The X coordinate of the mouse pointer in local (DOM content) coordinates.
The Y coordinate of the mouse pointer in local (DOM content) coordinates.
The button number that was pressed when the mouse event was fired: Left button=0, middle button=1 (if present), right button=2. For mice configured for left handed use in which the button actions are reversed the values are instead read from right to left.
The buttons being pressed when the mouse event was fired: Left button=1, Right button=2, Middle (wheel) button=4, 4th button (typically, "Browser Back" button)=8, 5th button (typically, "Browser Forward" button)=16. If two or more buttons are pressed, returns the logical sum of the values. E.g., if Left button and Right button are pressed, returns 3 (=1 | 2). More info.
The amount of pressure applied to a touch or tabdevice when generating the event; this value ranges between 0.0 (minimum pressure) and 1.0 (maximum pressure).