Thanks for your edit so that other users now know that option and can go about trouble shooting more specifically.
I just wanted to chime in here, that ever since i followed the step by step provided guides on the forums on; 1) the correct divX player to download, then if there wasn't audio; i grabbed the codec pack offered here
. After that I constantly update my FireFox (which if your using FF, you should be running v.3.6.12) as of 11/4/2010 and i've yet to have half these problems a lot of users are facing. Im sorry some of you are getting odd errors, or dealing with simply stupid, over reactive AV progs telling you this and that is malware or viruses....because that's just how over the top AV progs work IMO.
Just remember, be specific as to what you did or installed before your issue started happening, when was it working and what changed since then. Helps really clarify some of your issues for the people like myself and a nice handful of others within the community willing to help you guys and gals.