Firefox suddenly stopped playing audio on all web-sites.

I assume windows since no info was provided. Check here. see screenshot Look in device manager, see who makes the audio component, and reinstall or update the driver.

Sorry, not windows Kubuntu 64bit

Show the issue. see screenshot I cannot replicate the issue. Try downloading Firefox from Mozilla, run firefox-bin from the folder and see if you have the same issue. https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Operating System: openSUSE Tumbleweed 20241111 KDE Plasma Version: 6.2.3 KDE Frameworks Version: 6.8.0 Qt Version: 6.8.0 Kernel Version: 6.11.6-2-default (64-bit) Graphics Platform: X11 Processors: 16 × AMD Ryzen 7 5825U with Radeon Graphics Memory: 62.1 GiB of RAM Graphics Processor: AMD Radeon Graphics Manufacturer: HP Product Name: HP ProBook 455 15.6 inch G9 Notebook PC

Hi, I downloaded as you suggested; extracted to the desktop; ran firefox-bin from the folder; changed autoplay setting from 'block audio' (why is that default?) to 'allow audio and video'. Still no sound.

Operating System: Kubuntu 22.04 KDE Plasma Version: 5.24.7 KDE Frameworks Version: 5.92.0 Qt Version: 5.15.3 Kernel Version: 5.15.0-84-generic (64-bit) Graphics Platform: X11 Processors: 8 × Intel® Core™ i7-4770K CPU @ 3.50GHz Memory: 15.5 GiB of RAM Graphics Processor: Mesa Intel® HD Graphics 4600

Show pics of you audio settings. I'm not having any issues. How about running a live usb stick with your OS of choice to see if you still have issues with sound. I have another laptop running KDE 5 and also no issues with sound.

Are these the settings you want?

Nope. See my screenshots above. If you're not getting audio from your distro version and Mozilla Firefox, sounds like an system / OS issue. What happens with a live usb stick?