Avast Online Security is blocking access to embedded videos on SNY.tv and Breitbart.com when using FireFox Version 26. When I disable Avast Online Security addon in Firefox videos are displayed and I’m able to select and play videos. Its also happening on other sites.
You could play with allowing the various anti tracking catagories that you currently have enabled in the AOS and see whether that makes any difference. Some sites will not operate properly unless you let them track you. Or you could do what many of us have done, simply disable or even uninstall the AOS Firefox extension. You are still protected by the web shield.
Blocking tracking and ads are tricky. Block certain ads can break sites. Adblock plus solves this problem by selectively whitelisting certain elements. I just visited your site and tried the video and adblock plus whitelisted 9 object subrequests and scripts to allow the video to play. To test, I override one of the whitelist items and that was enough to stop the video from playing.
Such whitelisting has to be manually added rule by rule in their filter list sometimes for each specific site, which adblock filter list maintainers do every day, so it is a labor intensive process. You can’t just make a list that and add all known tracking/ad companies and not break sites.
I thought the Avast addon would use Easy privacy filter list of Adblock Plus to stop tracking b/c the previous Avast Adblock addon used those filter list, but I guess not. If they did you wouldn’t be running into these problems, it seems that Avast uses are more general list and blocking more indiscriminately which means you will continue to encounter these problems.