Muter is a firefox extension that helps you mute the entire browser.
It won't stop videos and audios playing when muting.
By default, a button will be placed in the addon bar. Click the button
to mute and click again to cancel muting.
Thanks to the following people for their excellent translations.
Dutch: markh van BabelZilla.org
Japanese: beiwaiMM (尧七目) newsmth.net
Polish: Leszek(teo) ŻyczkowskiCopy
French: Jim Courbron, Jojaba - BabelZilla
Spanish: Ricardo A. Rivas (rivica at gmail dot com)
Lithuanian: Algimantas Margevičius
Swedish: Mikael Hiort af Ornäs
German: erglo (de)
Catalan: Adrià Laviós
Greek: ilias@Greece, Sonickydon