I am running Avast Internet Security 12.1.2272 (build 12.1.3076.6) with the latest virus definitions and I am unable to view any pages of the AT&T website with the Avast Online Security plugin version 10.3.3.44 enabled. I have tried this in both Firefox 47.0.1 and Chrome 51.0.2704.106 m. If I disable the plugin I can freely browse any page of the AT&T website. As soon as I re-enable the plugin I cannot view the homepage or any other pages I try browsing directly too.
I have just tried connecting to -https://www.att.com and no issues reported. Using the latest avast free version, Firefox 47.0.1 with AOS add-on enabled (image1) with NoScript enabled and allowed for att.com, etc.
See image3 for my Avast Online Security settings. I haven’t got the Do Not Track option enabled, I just wonder if that could have an effect on att.com if enabled.