The Tor Browser / file revision

 // Q: But who shall debug the debuggers?  A: jimb

 var log = '';

 function addDebug(g, id) {

     var debuggerGlobal = newGlobal();

     debuggerGlobal.debuggee = g;

     debuggerGlobal.id = id;

     debuggerGlobal.print = function (s) { log += s; };

     debuggerGlobal.eval(

         'var dbg = new Debugger(debuggee);\n' +

         'dbg.onDebuggerStatement = function () { print(id); debugger; print(id); };\n');

     return debuggerGlobal;

 }

 var base = newGlobal();

 var top = base;

 for (var i = 0; i < 8; i++)  // why have 2 debuggers when you can have 8

     top = addDebug(top, i);

 base.eval("debugger;");

 assertEq(log, '0123456776543210');