uBlock is an adblocker, uMatrix has finely grained matrix controls for which http requests are even allowed to go through and requires tuning for most sites. I like having both :)
To do this In Firefox:
1) Type 'about:config' in your address bar
2) Set 'media.peerconnection.enabled' value to 'false'. (The Default value is 'true')
Not just voice/video but text. That said, I'm not sure how useful the P2P aspects of text are, but being able to send files directly would be a nice ability.