Chrome natively shows audio indicators for music playing tabs in its browser, Firefox users miss this feature, fortunately, Noise Control add-on now shows audio indicators for HTML5 video or audio playing tabs in the Firefox browser. You can also mute such video by clicking on the icon in that tab.
READ:Chrome Now Lets You Mute That Audio Playing Tab
How to Mute Multiple Tabs at Once in Chrome?
Noise Control adds Per-tab Audio indicators to Firefox with Click-to-mute functionality
Yesterday released Firefox 37 plays most videos on YouTube with HTML5 video player by default and this extension also “shows an icon when a plugin (such as Flash) is active on a page, because there’s no way to tell if a plugin is making noise.”