gistfile1.txt

    var window = gBrowser.selectedBrowser.contentWindow;
    var doc = window.document;
    var sandbox = new Components.utils.Sandbox(window);
    sandbox.window = window;
    sandbox.document = doc.wrappedJSObject ? doc.wrappedJSObject : doc;
    sandbox.navigator = window.navigator;
    sandbox.__webdriverParams = [{"foo": "bar", "goo":[1,2]}];

    try {
      var scriptSrc = 'with(window) { ' +
                      ' var __webdriverFunc = function(){ ' +
                      '         return arguments[0].foo;' +
                      '};' +
                      '__webdriverFunc.apply(null, __webdriverParams); }';
        Components.utils.evalInSandbox(scriptSrc, sandbox);
      
    } catch (e) {
      throw e
    }