The Tor Browser / file revision

 // The .environment of a function Debugger.Object is an Environment object.

 var g = newGlobal()

 var dbg = Debugger(g);

 var hits = 0;

 g.h = function () {

     var frame = dbg.getNewestFrame();

     var fn = frame.eval("j").return;

     assertEq(fn.environment instanceof Debugger.Environment, true);

     var closure = frame.eval("f").return;

     assertEq(closure.environment instanceof Debugger.Environment, true);

     hits++;

 };

 g.eval("function j(a) {\n" +

        "    var f = function () { return a; };\n" +

        "    h();\n" +

        "    return f;\n" +

        "}\n" +

        "j(0);\n");

 assertEq(hits, 1);