Hi Tom
I don’t see the issue from the chrome inspect element tool however I do see it from the chrome browser (firefox) as shown here.
https://1drv.ms/f/s!AjEGKOtzUwy1_V0vJGvX4lFcvekS
I can also make chrome (firefox) show the sites the same as http://responsivepx.com does. http://www.isresponsive.com also provides the same result.
I just sent screenshots of your site as the add-ons page provides a good example of what i mean.
Cheers