The Tor Browser / file revision

 // Storing a property on a Debugger.Object protects it from GC as long as the

 // referent is alive.

 var g = newGlobal();

 var N = g.N = 3;

 var dbg = Debugger(g);

 var i = 0;

 dbg.onDebuggerStatement = function (frame) {

     frame.arguments[0].id = i++;

 };

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

 g.eval("var arr = [], j; for (j = 0; j < N; j++) arr[j] = {};");

 g.eval("for (j = 0; j < N; j++) f(arr[j]);");

 assertEq(i, N);

 gc(); gc();

 i = 0;

 dbg.onDebuggerStatement = function (frame) {

     assertEq(frame.arguments[0].id, i++)

 }

 g.eval("for (j = 0; j < N; j++) f(arr[j]);");

 assertEq(i, N);