Comment 29 for bug 858466

Same bug happened to me but I found an easy way to resolve it at least for my case: In the sound settings I switch to the "Hardware" tab. There, for me, two devices are shown: "RV710/730" and "Internal Audio". If for "RV710/730" I switch the profile from "HDMI profile" to "Off" (thus disabling the device) everything works fine (reproducible). To me it seems as firefox/flash just takes the first available device it can find no matter what device it is. HTH

My system:
Samsung N720-Auro (Stievo)
Ubuntu 11.10 (Linux 3.0.0-19-generic #33-Ubuntu SMP Thu Apr 19 19:05:14 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux)

Installed packages:
firefox 12.0+build1-0ubuntu0.11.10.1
pulseaudio 1:1.0-0ubuntu3.1
flashplugin-installer 11.2.202.235ubuntu0.11.10.1