openLocationLastURL.jsm
(bug 953124) the openlocationlasturl.jsm javascript code module lets you set and retrieve the url most recently opened using the "open location" option in the file menu.
... to use this, you first need to import the code module into your javascript scope: components.utils.import("resource:///modules/openlocationlasturl.jsm"); once you've imported the module, you can then use the openlocationlasturl object it exports.

JavaScript code modules
openlocationlasturl.jsm provides access to the last url opened using the "open location" option in the file menu.