NILAt work I have the sound of my laptop not muted because I need sound
from time to time. But browsing the internet with Firefox can sometime
trigger some undesired sound, very boring in the office. There is the
extension **Mute Tab** to auto-mute a new tab on Firefox so it won't
play sound. The auto-mute must be activated in the plugin options,
it's un-checked by default.
You can find it here, no restart required: [Firefox Mute Tab addon](https://addons.mozilla.org/fr/firefox/addon/mute-tab)
I also use **FlashStopper** which block by default flash and HTML5
videos, so you can click on it to activate them, it doesn't autoplay.
[Firefox FlashStopper addon](https://addons.mozilla.org/en-US/firefox/addon/flashstopper/)