Tor Browser uses its own instance of the tor daemon and communicates with it using the Tor control port on 127.0.0.1; the protocol is documented here: https://gitweb.torproject.org/torspec.git/tree/control-spec.txt tor-launcher is a Firefox extension that uses this protocol to manage the tor daemon used by Tor browser. It provides the control and communications glue used by the torbutton add-on to e.g. display the nodes in the current circuit, change the tor configuration, etc.
WWW: https://www.torproject.org
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