The Tor Browser / file revision

 // Setting onPop handlers from breakpoint handlers works.

 var g = newGlobal();

 g.eval("function f(){ return 'to normalcy'; }");

 var dbg = new Debugger();

 var gw = dbg.addDebuggee(g);

 var log;

 // Set a breakpoint at the start of g.f

 var gf = gw.makeDebuggeeValue(g.f);

 var fStartOffset = gf.script.getLineOffsets(gf.script.startLine)[0];

 gf.script.setBreakpoint(fStartOffset, {

     hit: function handleHit(frame) {

         log += 'b';

         frame.onPop = function handlePop(c) {

             log += ')';

             assertEq(c.return, "to normalcy");

         };

     }

 });

 log = "";

 assertEq(g.f(), "to normalcy");

 assertEq(log, "b)");