Debian 8.0 (Jessie)
Sound system: ALSA
The soultion I found was to change /etc/asound.conf file.
$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: SB [HDA ATI SB], device 0: ALC887-VD Analog [ALC887-VD Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
/etc/asound.conf that fixed no sound problem of Firefox v40.
defaults.pcm.card 0
defaults.pcm.device 0
defaults.ctl.card 0
Previous /etc/asound.conf
pcm.!default {
type hw
card SB
}
ctl.!default {
type hw
card SB
}
