Videos and Avast Internet Security add-on

I use Firefox 25.1 with Avast Pro 2104.9.0.2008 and Windows 7. When I go to my home page, which is http://att.yahoo.com/ the news videos do not show. It is completely white where the videos should be. The only way I can get it to work is to disable the Avast Internet Security Add-on and restart Firefox. It is the same way with Internet Explorer. Is there a setting or something I can change that will make the videos work without having to disable this add-on? I asked this question on the Avast forum but I haven't received any replies. I use WOT but it was nice having a second opinion. If I am slow to answer any questions, it will be because I don't get emails notifying me of replies to my threads that I have subscribed too. This service has quit working although my email address is correct on my profile. Thank you for your time and help.