use correct function name

src/chrome/content/torbutton.js

@@ -2221,7 +2221,7 @@ function torbutton_update_thirdparty_prefs() {
       m_tb_prefs.setIntPref("network.cookie.cookieBehavior", 0);
     }
 
-    pref("security.enable_tls_session_tickets", !mode);
+    m_tb_prefs.setBoolPref("security.enable_tls_session_tickets", !mode);
 
     // Force prefs to be synced to disk
     var prefService = Components.classes["@mozilla.org/preferences-service;1"]