diff --git a/common/modules/util.jsm b/common/modules/util.jsm
index 1fd69c10..87d4a279 100644
--- a/common/modules/util.jsm
+++ b/common/modules/util.jsm
@@ -1128,7 +1128,7 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
             if (~["boolean", "number"].indexOf(typeof data) || data === null)
                 res.push(String(data));
             else if (isinstance(data, ["String", _]))
-                res.push(JSON.stringify(String(data)));
+                res.push(JSON.stringify(data));
             else if (isArray(data)) {
                 if (data.length == 0)
                     res.push("[]");