http://www.xulplanet.com/tutorials/xultu/progress.html http://www.xulplanet.com/reference/elemref/ref_progressmeter.html A meter which can be used to display the progress of a lengthy operation. It is drawn as a bar that is filled as the operation completes. In addition, an undeterminate progressmeter may be created by setting the mode attribute. This is used when the length of time to complete an operation is not known beforehand. nsIAccessibleProvider A determined progressmeter is used in cases where you know how long an operation will take. Undeterminate progressmeters can be used when you don't and will typically be drawn as a spinning barber pole. The progress meter uses its value attribute to determine the amount of the bar that is filled in. The progressmeter is undeterminate. A percentage value that specifies the amount of the meter that is filled in. Because it is a percentage, it ranges from 0 to 100. Returns the accessibility object for the progressmeter.