Mozilla dropped support for ALSA (Advanced Linux Sound Architecture) and is now requiring Linux users to have installed the PulseAudio library to support audio playback inside Firefox. Many Firefox users on Linux were left without the ability to play sound in their browser after updating to Firefox 52, released last week. Mozilla didn’t warn Firefox users about this change and had no forewarning. Mozilla has now set up a support page detailing the issue and is prompting ALSA-only Linux users via a popup that reads “To play audio
Source: security