Youtube video freezes while the audio repeats (Firefox)

After upgrading to the latest Firefox version, I'm experiencing a wierd problem while watching any youtube videos.

Basically, during some point in playback, the video freezes and the audio repeats 10~15 seconds behind. Once the repeat is done, the video unfreezes and it continues playing. Its been happening for every videos I've played and I just can't find a solution for this problem.

Things I've tried:

- For Firefox:

      > Disabled hardware acceleration via option

      > Deleted cache

      > Disabled all addons and plugins (except for adobe flash)

      > Uninstall and reinstall the browser

- For Flash player:

      > Also disabled hardware acceleration via video option

      > Cleared "all site datas and settings"

      > Uninstall and resintall the flash player

- For GPU, I've checked that I had the latest driver installed

Here's the information you might need to know:

- Windows 7 64bit

- AMD HD7900 series GPU

- Firefox version 26.0

- Flash player version 12.0.0.43

It's getting very annoying lately and I would appreciate it if I could get some solutions to try out. Also, please don't recommend me to use another browser because I'm not going to change my browser just to avoid this problem. More so, please don't recommend me to downgrade Firefox and flash player versions as well.

Thank you.

P.S I would like to politely ask the mods not to mark any reply with solution as ""answer" until the actual problem has been solved. There were cases where people asked questions (including me) and mods will mark one of the reply as answer which, that answer didn't actually solved the problem for some people. As a result, sometimes when we further ask for help, we don't get any replies which results in dead thread.

That said, please correct me if I'm wrong about this though I would appreciate it if you consider it.