You can audit it for backdoors and build the browser bundle yourself. https://gitweb.torproject.org/tor.git/tree/refs/heads/release-0.2.4:/src/or https://gitweb.torproject.org/vidalia.git/tree/refs/heads/master:/src/vidalia http://ftp.mozilla.org/pub/mozilla.org/firefox/releases/17.0.8esr/source/ https://gitweb.torproject.org/torbrowser.git/tree/refs/heads/maint-2.4:/src/current-patches/firefox