My audio works everywhere except in my browsers - a little help?

Last week, I noticed that I had suddenly lost audio in YouTube. The video plays fine, just no sound. I verified that the sound bar was up and not muted on YouTube, as well as in my mixer. In fact, I can see the audio modulating in my mixer. It seems as though it's only in my browsers that I have an issue, because my sound tests okay from the Control Panel and I'm able to have audio and video conversations in Skype. I also tried a Google Plus Hangout last night with a friend, and that worked, too. But YouTube, Vimeo and Facebook videos have no audio at all.

I've exhausted so many suggested checks and solutions that I can't even remember how many... easily dozens. The only thing I've found that is odd is that the Openh264 Codec from Cisco was saying "will be updated shortly" until just an hour or so ago (for the last couple of days). But now that it's updated (and still activated), nothing has changed. 

I see that a LOT of people have been having this same problem for the last several years. The problems they report (for the few that were able to resolve the issue) differ, but the symptoms seem to be the same. They all seem to stem from some sort of flash configuration issue. I'm semi-literate with software configuration, at best, so I would sure appreciate any help anyone can offer.

• Operating system version - Win7 Ultimate, X64, SP1
• Web browser and version - Firefox 37.0.1
• http://kb2.adobe.com/cps/155/tn_15507.htmlFlash Player version - 17.0.0.169