The Tor Browser / file revision

 // Frame.prototype.this in non-strict-mode functions, with primitive values

 function classOf(obj) {

     return Object.prototype.toString.call(obj).match(/^\[object (.*)\]$/)[1];

 }

 var g = newGlobal();

 var dbg = new Debugger(g);

 var hits = 0;

 dbg.onDebuggerStatement = function (frame) {

     hits++;

     assertEq(frame.this instanceof Debugger.Object, true);

     assertEq(frame.this.class, g.v == null ? classOf(g) : classOf(Object(g.v)));

 };

 g.eval("function f() { debugger; }");

 g.eval("Boolean.prototype.f = f; v = true; v.f();");

 g.eval("f.call(v);");

 g.eval("Number.prototype.f = f; v = 3.14; v.f();");

 g.eval("f.call(v);");

 g.eval("String.prototype.f = f; v = 'hello'; v.f();");

 g.eval("f.call(v);");

 g.eval("v = undefined; f.call(v);");

 g.eval("v = null; f.call(v);");

 assertEq(hits, 8);