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Type: boolean
New in Firefox 40.
Indicates that a tab is selected. In multiprocess Firefox, the selected attribute is set synchronously, as soon as the user (or code) selects a tab. The visuallyselected attribute is set asynchronously, once the browser has switched to the selected tab. See tab selection in multiprocess Firefox for more details.
If your code needs to apply some styling to the currently selected tab, this is the attribute you should use from Firefox 40 onwards.
This value is read-only. To change the selection, set either the selectedIndex or selectedItem property of the containing element.