Open Dom Inspector at this node from Inspect on context menu. Dom Inspector must already be installed. Handy for checking both page for web developers and chrome for extension developers. Adds menu item to many existing context menus. Stand alone "Inspect" context popup for many items that normally have no context menu including menus.
Dom Inspector once included with Firefox available as a separate addon https://addons.mozilla.org/firefox/addon/dom-inspector-6622/
Double context click can open extra popup. Stand alone "Inspect" context popup may not line up with click.