The Tor Browser / file revision

 // Debugger.Object.prototype.makeDebuggeeValue creates only one

 // Debugger.Object instance for each debuggee object.

 var g = newGlobal();

 var dbg = new Debugger();

 var gw = dbg.addDebuggee(g);

 g.eval("var x = { 'now playing': 'Joy Division' };");

 g.eval("var y = { 'mood': 'bleak' };");

 wx = gw.makeDebuggeeValue(g.x);

 assertEq(wx, gw.makeDebuggeeValue(g.x));

 assertEq(wx === g.x, false);

 assertEq("now playing" in wx, false);

 assertEq(wx.getOwnPropertyNames().indexOf("now playing"), 0);

 wx.commentary = "deconstruction";

 assertEq("deconstruction" in g.x, false);

 wy = gw.makeDebuggeeValue(g.y);

 assertEq(wy === wx, false);

 wy.commentary = "reconstruction";

 assertEq(wx.commentary, "deconstruction");

 // Separate debuggers get separate Debugger.Object instances, but both

 // instances' referents are the same underlying object.

 var dbg2 = new Debugger();

 var gw2 = dbg2.addDebuggee(g);

 w2x = gw2.makeDebuggeeValue(g.x);

 assertEq(wx === w2x, false);

 w2x.defineProperty("breadcrumb", { value: "pumpernickel" });

 assertEq(wx.getOwnPropertyDescriptor("breadcrumb").value, "pumpernickel");

 // Non-objects are already debuggee values.

 assertEq(gw.makeDebuggeeValue("foonting turlingdromes"), "foonting turlingdromes");

 assertEq(gw.makeDebuggeeValue(true), true);

 assertEq(gw.makeDebuggeeValue(false), false);

 assertEq(gw.makeDebuggeeValue(null), null);

 assertEq(gw.makeDebuggeeValue(1729), 1729);

 assertEq(gw.makeDebuggeeValue(Math.PI), Math.PI);

 assertEq(gw.makeDebuggeeValue(undefined), undefined);