It's possible there is no audio on those clips.

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

You can check the Web Console (Tools -> Web Developer) for media related messages

• https://developer.mozilla.org/en/Tools/Web_Console
• https://developer.mozilla.org/en/Tools/Network_Monitor

If necessary use "Ctrl+F5" or "Ctrl+Shift+R" (Mac: Command+Shift+R) to reload the page and bypass the cache to generate a fresh log.

insom63 said

When I am on YouTube everything is fine except one of my subscriptions has no audio. If I watch the same subscription on my TV, the audio is fine.

Link?

~Pj