This is an extension for Pale Moon web browser, which exposes noisy tabs containing audio or video elements. It simply shows indicator icons for tabs which play sounds, but has also a feature to mute them. In addition, it can prevent automatic media playback for background tabs or, at least, try to do it as soon as possible.
The extension works only with HTML5 media elements. Flash is not supported.
Whenever some HTML5 media element starts playing sound inside a tab, an indicator icon should appear after its title. You can mute and unmute such a tab by clicking on that indicator. It can also be done with a Ctrl+M keyboard shortcut while browsing that tab.
Appearance of the indicator icon can be changed in the extension's preferences. There are several themes available. You can also enable or disable the keyboard shortcut and the option to prevent automatic media playback for background tabs.