Ubuntu Firefox Won't Play Sounds

I use Ubuntu 22.04 and Firefox on my laptop, because I am convinced of the open-source-software idea.
Today, suddenly Firefox did not play sounds any more. Previous video worked fine, next was silent. Tried other videos, all were silent. Rebooted the machine, started Firefox, played a video - no sound.

First I checked the Ubuntu volume control, which is on upper right corner of the task bar. It was not muted.

Next I checked my computer's audio hardware via Ubuntu menu "Settings" (right upper side of primary screen). When you go there and click "Sound", there is a section "Output" on the right side where you have a "Test" button. If you click that, a dialog comes up that lets you test any speaker of your hardware. Both built-in speakers of my laptop worked fine! Besides, there is also a volume control in the "Sound" settings, but this wasn't muted.

Then I started another browser, which was Chrome. For many problems it is useful to have more than one browser installed. I pasted the video URL from Firefox into its address line, and - there was sound!

So what makes Firefox be silent from one moment to the next? What I didn't know is that you can switch off video and/or audio, for all websites, in Firefox's "Settings". I followed the instructions of a mozilla page about this.

Toggle Video and Audio in Firefox

• Click the Firefox menu button (top right) and select "Settings".


• Enter "autoplay" in the "Find in Settings" text field, or select "Privacy & Security" and scroll down to the "Permissions" section.


• In the "Autoplay" line, click the right side "Settings..." button, a dialog comes up.


• Use the "Default for all websites" drop-down menu to select how you want Firefox to handle audio and video. Below the drop-down is a list where you can do that for specific websites.


• In the drop-down, select "Allow Audio and Video", then click the "Save Changes" button.

It turned out that "Block Audio" was selected in my Firefox. How can this happen? Maybe some keyboard shortcut that I triggered accidentally? I selected "Allow Audio and Video" as default, clicked the "Save Changes" button, and - sound was back again in Firefox!