config: document enableFirefoxSimulcast

config.js

@@ -12,6 +12,10 @@ var config = { // eslint-disable-line no-unused-vars
         //focus: 'focus.jitsi-meet.example.com', // defaults to 'focus.jitsi-meet.example.com'
     },
     testing: {
+        /**
+         * Enables experimental simulcast support on Firefox.
+         */
+        enableFirefoxSimulcast: false,
         /**
          * P2P test mode disables automatic switching to P2P when there are 2
          * participants in the conference.