diff -r 000000000000 -r 6474c204b198 modules/libpref/test/unit/test_bug506224.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/libpref/test/unit/test_bug506224.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,29 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/  */
+
+function run_test() {
+  const Cc = Components.classes;
+  const Ci = Components.interfaces;
+  const PREF_NAME = "testPref";
+
+  var ps = Cc["@mozilla.org/preferences-service;1"]
+           .getService(Ci.nsIPrefService);
+  var prefs = ps.getDefaultBranch(null);
+  var userprefs = ps.getBranch(null);
+
+  prefs.setCharPref(PREF_NAME, "test0");
+  prefs.lockPref(PREF_NAME);
+  do_check_eq("test0", userprefs.getCharPref(PREF_NAME));
+  do_check_eq(false, userprefs.prefHasUserValue(PREF_NAME));
+
+  var file = do_get_profile();
+  file.append("prefs.js");
+  ps.savePrefFile(file);
+
+  prefs.unlockPref(PREF_NAME);
+  prefs.setCharPref(PREF_NAME, "test1");
+  ps.readUserPrefs(file);
+
+  do_check_eq("test1", userprefs.getCharPref(PREF_NAME));
+  do_check_eq(false, userprefs.prefHasUserValue(PREF_NAME));
+}