Failing test case of Debugger.Frame.onPop when the execution of a frame is about to end (i.e. when the return value is displayed in the DevTools or in Firebug + JSD2)

failing-test-case-debugger-frame-onPop.js

/*
  Failing test case:
     1. Open this page: https://getfirebug.com/tests/head/script/4213/issue4213.html
     2. With the DevTools, set a breakpoint at line 4 of issue4213-1.js (in myFunc1)
     3. Click on the "Execute Test" button of the webpage
       |=> the breakpoint is hit
     4. Step over
       |=> the return value is displayed
     5. Run this in Scratchpad (environment = browser)
     6. Resume the execution
  
  Working test case: same as above without step 4.
*/

var dbgMap = new WeakMap();

var getDebugger = function(wrappedWin = gBrowser.selectedBrowser.contentWindow)
{
    try
    {
        var jsDebugger = {};
        Cu.import("resource://gre/modules/jsdebugger.jsm", jsDebugger);

        var global = Cu.getGlobalForObject({});
        jsDebugger.addDebuggerToGlobal(global);

        var dbg = new global.Debugger();

        var win = XPCNativeWrapper.unwrap(wrappedWin);
        dbg.addDebuggee(win);
        
        if (dbgMap.has(win))
           return dbgMap.get(win);

        // Register 'onNewGlobalObject' hook to append dynamically created iframes
        // into the debugger as debuggees.
        dbg.onNewGlobalObject = function(global)
        {
            // xxxHonza: use timeout to avoid crash, see:
            // https://bugzilla.mozilla.org/show_bug.cgi?id=885301
            setTimeout(addNewDebuggee.bind(this, dbg, win, global));
        }
        
        dbgMap.set(win, dbg);

        return dbg;
    }
    catch (err)
    {
        alert(err);
    }
};

var dbg = getDebugger();


var frame = dbg.getNewestFrame();

frame.onPop = frame.onResume = frame.onStep = function()
{
    return frame.eval("42");
}