When a popup attached via the popup or context attributes is opened, the XUL document's popupNode property is set to the node that was clicked on. This will be the target of the mouse event that activated the popup. If the popup was opened via the keyboard, the popup node may be set to null. Typically, this property will be checked during a popupshowing event handler for a context menu to initialize the menu based on the context.
The HTMLCanvasElement.height property is a positive integer reflecting the height HTML attribute of the <canvas> element interpreted in CSS pixels. When the attribute is not specified, or if it is set to an invalid value, like a negative, the default value of 150 is used.
The HTMLCanvasElement.mozOpaque property is a Boolean reflecting the moz-opaque HTML attribute of the <canvas> element. It lets the canvas know whether or not translucency will be a factor. If the canvas knows there's no translucency, painting performance can be optimized.
The HTMLCanvasElement.width property is a positive integer reflecting the width HTML attribute of the <canvas> element interpreted in CSS pixels. When the attribute is not specified, or if it is set to an invalid value, like a negative, the default value of 300 is used.