How to find which Firefox tab is playing audio without installing extensions?

On Chrome/Chromium/Brave there's a button that tells you which tabs are playing audio. On Firefox I can't find the same thing.

The best I can do is going to task manager and seeing which tab is using more CPU which normally is the one that is playing something.

Any solution for this?

Solution 1:

Since Firefox 89 it's spelled out explicitly below the tab title:

Versions 42 through 88 used a speaker icon next to the × button, just like Chrome-likes do.

Solution 2:

Apparently another indicator was added in Firefox 91 that is visible even on tiny tabs:

The speaker badge on the tab icon appears when a tab is playing sounds. It can be clicked to (un)mute the tab.