Audio does not work in Firefox - "Not connected to the PulseAudio server"

Hi,

I am using System Rescue 12.01 and I access YouTube using Firefox but there is no sound. There is an oblique line over the volume icon in the taskbar.

When I hover the cursor over the volume icon in the taskbar, the tooltip message "Not connected to the PulseAudio server" is shown. If I left-click the volume icon and choose "Audio mixer..." a window with the title "Volume Control" appears having the text "Establishing connection to PulseAudio. Please wait...". It shows a loading cursor but nothing happens. Running the pavucontrol command in the Terminal has the same effect.

Playing a sample .wav file in the Terminal works, however, using the following command:

aplay /usr/share/sounds/alsa/Rear_Center.wav

Running alsamixer in the Terminal shows the following:

Card: HDA Intel
Chip: Realtek ALC269

Running lspci | grep -i audio in the Terminal shows the following:

00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03)

I do not know why sound is not working in Firefox. Hope you can help me.

Best regards,

John