diff --git a/common/modules/base.jsm b/common/modules/base.jsm
index e00211ad..3bb93783 100644
--- a/common/modules/base.jsm
+++ b/common/modules/base.jsm
@@ -634,7 +634,8 @@ function update(target) {
             let desc = Object.getOwnPropertyDescriptor(src, k);
             if (desc.value instanceof Class.Property)
                 desc = desc.value.init(k, target) || desc.value;
-            if (typeof desc.value == "function" && Object.getPrototypeOf(target)) {
+
+            if (typeof desc.value === "function" && target.__proto__) {
                 let func = desc.value.wrapped || desc.value;
                 func.__defineGetter__("super", function () Object.getPrototypeOf(target)[k]);
                 func.superapply = function superapply(self, args)
diff --git a/common/modules/prefs.jsm b/common/modules/prefs.jsm
index c287dab8..38c26ed0 100644
--- a/common/modules/prefs.jsm
+++ b/common/modules/prefs.jsm
@@ -228,9 +228,7 @@ var Prefs = Module("prefs", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference])
         case "string":
             assertType(Ci.nsIPrefBranch.PREF_STRING);
 
-            let supportString = Cc["@mozilla.org/supports-string;1"].createInstance(Ci.nsISupportsString);
-            supportString.data = value;
-            this.branch.setComplexValue(name, Ci.nsISupportsString, supportString);
+            this.branch.setComplexValue(name, Ci.nsISupportsString, services.String(value));
             break;
         case "number":
             assertType(Ci.nsIPrefBranch.PREF_INT);