So everything was working perfectly on my system. I have Debian SID, with the debian-multimedia repos and liquorix repos for kernels. Flash worked perfectly one boot, then the next boot the video still works perfectly but no audio. I found several "fixes" on the web, including creating .asoundrc in your home directory and another that said to neither of those have done anything. Have tried using both the flashplugin-nonfree and flashplayer-mozilla, same thing on either. ALL other sound works, smplayer, amarok, system sounds, etc.

1. Test in another browser to determine whether it's a system-wide or Firefox problem.

2. Post the contents of your /usr/lib/mozilla/plugins directory.