diff -r 000000000000 -r 6474c204b198 modules/libpref/test/unit_ipc/test_initial_prefs.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/libpref/test/unit_ipc/test_initial_prefs.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,18 @@
+const Ci = Components.interfaces;
+const Cc = Components.classes;
+
+function isParentProcess() {
+    let appInfo = Cc["@mozilla.org/xre/app-info;1"];
+    return (!appInfo || appInfo.getService(Ci.nsIXULRuntime).processType == Ci.nsIXULRuntime.PROCESS_TYPE_DEFAULT);
+}
+
+function run_test() {
+  if (isParentProcess() == false) {
+      var pb = Cc["@mozilla.org/preferences-service;1"].getService(Ci.nsIPrefBranch);
+      pb.setBoolPref("Test.IPC.bool", true);
+      pb.setIntPref("Test.IPC.int", 23);
+      pb.setCharPref("Test.IPC.char", "hey");
+
+      run_test_in_child("test_existing_prefs.JS");
+  }
+}
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