The Tor Browser / file revision

 // clearBreakpoint clears breakpoints for the current Debugger object only.

 var g = newGlobal();

 var hits = 0;

 var handler = {

     hit: function (frame) {

         hits++;

         frame.script.clearBreakpoint(handler);

     }

 };

 function attach(i) {

     var dbg = Debugger(g);

     dbg.onDebuggerStatement = function (frame) {

         var s = frame.script;

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

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

             s.setBreakpoint(offs[i], handler);

     };

 }

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

     attach(i);

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

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

        "Math.sin(0);\n");   // line0 + 2

 assertEq(hits, 4);