You may have already encountered some sound problems while playing several flv videos opened in different tabs. If you stop playing one of them for a while and then try to watch it again, you are unable to understand the sound that comes from the video.
Here is one solution :
In the file /etc/iceweasel/iceweaselrc, replace the line ICEWEASEL_DSP=”none” by ICEWEASEL_DSP=”aoss”
aoss is a simple wrapper script which facilitates the use of the ALSA OSS compatibility library.
To install it :
root@localhost:~#apt-get install alsa-oss