I've reinstalled FF, tried refreshing, and turning off ad blocker plus. Videos on Vimeo and Facebook don't play sound. Sound on computer is fine. Many (all?) youtube videos play just fine. Things may be complicated a bit because I am using Win Server 2008 r2 as my workstation. Google Chrome plays the same videos without a problem, isolating it to this particular installation of firefox. It COULD be related to OS issues, which complicates matters. Google search yields no similar problems for anyone else, which leaves me to again suspect the fact I'm using WinServ as the culprit. I tried downloading "Media Feature Pack for Windows 7 N with Service Pack 1 and Windows 7 KN with Service Pack 1 (KB968211) " but as you'll notice that is for Win 7, which is the closest thing to 2008 r2. It downloaded and stated that I had the wrong operating system, so... Firefox is up to date, add-ons are very few, and turning them off doesnt affect the issue. Any other debug/trouble shoot ideas?