RickK - 4:13 pm on Jul 3, 2013 (gmt 0)
You are getting this is because IE works different to Firefox. Firefox will load but it will not show the padlock to say the page is secure, when you view information in Firefox it will also say the page is partially encrypted. If you accept the IE prompt it will also kind off remove the padlock.
The reason this is happening is because you have external links or images going to
http://facebook.com as a quick example. Any HTTP link on a HTTPS page will cause it to not be fully secure.
Change all the hyperlinks and images to go over https and your page will work.
Let me know if you have any questions at all.