Created .asoundrc in my home directory:
# 48000 S16_LE 2ch (aplay -t raw -f dat)
Started firefox from the command line:
FLASH_ALSA_DEVICE=fileout firefoxConverted the raw file it to a wav file:
sox -r 48k -s -b 16 -c 2 out.raw out.wav...assuming that it's 48kHz sampling rate, 16bits and two channels stereo.