The Tor Browser / file revision

 // A breakpoint cleared during dispatch does not fire.

 // (Breakpoint dispatch is well-behaved even when breakpoint handlers clear other breakpoints.)

 var g = newGlobal();

 var dbg = Debugger(g);

 var log = '';

 dbg.onDebuggerStatement = function (frame) {

     var s = frame.script;

     function handler(i) {

         if (i === 1)

             return function () { log += i; s.clearBreakpoint(h[1]); s.clearBreakpoint(h[2]); };

         return function () { log += i; };

     }

     var offs = s.getLineOffsets(g.line0 + 2);

     var h = [];

     for (var i = 0; i < 4; i++) {

         h[i] = {hit: handler(i)};

         for (var j = 0; j < offs.length; j++)

             s.setBreakpoint(offs[j], h[i]);

     }

 };

 g.eval("var line0 = Error().lineNumber;\n" +

        "debugger;\n" +          // line0 + 1

        "result = 'ok';\n");     // line0 + 2

 assertEq(log, '013');