Also your QThread subclass implementation of the run function is missing the exec() call, so your Thread has no running eventloop. Have a look at "this link":http://qt-project.org/wiki/QThreads_general_usage .
In case the Html5ApplicationViewer instance is using any Gui class like e.g. QWebView you won't be able to run instances of this class in any other thread but the main thread. If that is what you wanted to do.