window.close @ MDN (Mozilla docs)
This method is only allowed to be called for windows that were opened by a script using the window.open method. If the window was not opened by a script, the following error appears in the JavaScript Console: Scripts may not close windows that were not opened by script.
W3C norm on HTML5 agrees :
The close() method on Window objects should, if the corresponding browsing context A is an auxiliary browsing context that was created by a script (as opposed to by an action of the user), and if the browsing context of the script that invokes the method is allowed to navigate the browsing context A, close the browsing context A (and may discard it too).