No sound on Firefox and Opera, but works on Chrome

Question

Ubuntu 18.04.2
Firefox Quantum 65.0.1

There is no sound from Firefox or Opera browsers when playing youtube videos etc. Chrome works fine. Desktop music/video player apps also work without any issues. Neither inbuilt speakers nor headphones work for the problematic browsers.

I've gone through the other posts that reported the same problem and tried all the solutions; didn't solve the issue.

• Pulse-audio is installed by default. Firefox and Opera show up in the list of applications under sound settings with their respective volume control though.

• Installing ubuntu-restricted-extras didn't help. I don't think it's a codec issue. Playing ogg/flac from wikipedia also makes no sound on firefox.
• Clearing cache as mentioned in firefox faq didn't help either.

Answer 1

The problem was, firefox and opera were streaming the audio to HDMI rather than to laptop speakers or headphones. This is despite selecting built-in audio as output device in sound settings app. There was no way to know this from sound settings app or any settings in the problematic browsers.

I had to install Pulse Audio Volume Control (pavucontrol). In addition to showing streams from apps, it has option to switch output device for each stream. Changing the settings for firefox and opera solved the issue.