The 29. january I got no sound when streeming video from Firefox. I checked the situation with VLC, another media player, which had no problems with the sound. I opened Windows "sound control settings" and chose to send the sound to the monitor (HDMI). Then I got sound from Firefox. When I sent the sound back to the original device, which is an USB Audio DAC, because I use an external amplifier, and my PC doesn't have the SP/DIF output. Again there were no sound from Firefox, but sound from VLC. In addition I started Microsoft Edge, and got sound! Which means that the problem is only with Firefox. Then I checked the time for the last Firefox update. It was january 28, the day before (or it could have been the same day), and the new version was: 147.0.2. That made me beleive that the cause of the problem was the software update. What else could have caused this problem ? I do not know how to fix this problem. I need help, otherwise I have to quit using Firefox, which I have been using for a decade without any problems. I am using Windows 11.