I have this problem in my Dapper and my nForce2 audio, but I can solve it putting FIREFOX_DSP="aoss" in /etc/firefox/firefoxrc and /etc/mozilla-firefox/mozilla-firefoxrc, and using the autoaudiosink for gstreamer 0.10. I'm always using the snd_intel8x0 alsa module.
I wonder if the best solution is to put the following by default in any Dapper installation:
1. FIREFOX_DSP="aoss" in /etc/firefox/firefoxrc and /etc/mozilla-firefox/mozilla-firefoxrc (by now it's set to "alsa09")
2. The alsa-oss package installed (by now it's not installed by default)
3. The autoaudiosink used by default for gstreamer (I think alsasink is used now instead)
Reading more under the comments shows that this does not interfere with esd sounds from the desktop and fixes the serious problem when Macromedia Flash calls /dev/dsp more than once when using libesd-alsa0.
sudo aptitude install alsa-oss
sudo gedit /etc/firefox/firefoxrc
Howto fix Firefox Flash Video Sound on Ubuntu Linux Dapper
technorati tags:Alsa, Ubuntu