Load website (vebview) using Firefox, Chrome or any other browser, How to cahange user-agent in QT 5

[JETY]

I am a beginner in QT. I have a code that loads Google Earth plugin in a windows. Unfortunatley, IE (internet Explorer) does not like Google Earth plugin like many others, so I would like to load it using Firefox.
I made some research and I found this "example":http://dipeshbhattarai.com/?p=48 and this "post":https://qt-project.org/forums/viewthread/21041 referring to the topic. Apparently I have to change the user agent to force Qwebview to use Firefox. The previous example is for QT 4 so it does not work anymore. I have been reading the QT API for "QNetworkRequest":http://qt-project.org/doc/qt-5/QNetworkRequest.html and "QWebView":http://qt-project.org/doc/qt-5/QWebView.html but I do not understand what I have to do.
Could anyone help me on that.
Thank you in advance.