http://www.xulplanet.com/reference/elemref/ref_resizer.html An element used for window resizing. If you place a custom resizing button inside the resizer, the user will be able to resize the window by dragging it. The resizer will send a command event after the resize is complete. The direction that the window is resized. Resized to the left. Resized to the right. Resized up. Resized down. Resized down and to the left. Resized down and to the right. Resized up and to the left. Resized up and to the right.