diff -r 000000000000 -r 6474c204b198 toolkit/components/contentprefs/tests/unit/test_unusedGroupsAndSettings.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/contentprefs/tests/unit/test_unusedGroupsAndSettings.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,52 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+var cps = new ContentPrefInstance(null);
+          
+function run_test() {
+  var uri1 = ContentPrefTest.getURI("http://www.domain1.com/");
+  var uri2 = ContentPrefTest.getURI("http://foo.domain1.com/");
+  var uri3 = ContentPrefTest.getURI("http://domain1.com/");
+  var uri4 = ContentPrefTest.getURI("http://www.domain2.com/");
+
+  cps.setPref(uri1, "one", 1);
+  cps.setPref(uri1, "two", 2);
+  cps.setPref(uri2, "one", 4);
+  cps.setPref(uri3, "three", 8);
+  cps.setPref(uri4, "two", 16);
+  
+  cps.removePref(uri3, "three"); // uri3 should be removed now
+  checkForUnusedGroups();
+  checkForUnusedSettings();
+
+  cps.removePrefsByName("two"); // uri4 should be removed now
+  checkForUnusedGroups();
+  checkForUnusedSettings();
+  
+  cps.removeGroupedPrefs();
+  checkForUnusedGroups();
+  checkForUnusedSettings();
+}
+
+function checkForUnusedGroups() {
+  var stmt = cps.DBConnection.createStatement(
+               "SELECT COUNT(*) AS count FROM groups " +
+               "WHERE id NOT IN (SELECT DISTINCT groupID FROM prefs)"
+             );
+  stmt.executeStep();
+  do_check_eq(0, stmt.row.count);
+  stmt.reset();
+  stmt.finalize();
+}
+
+function checkForUnusedSettings() {
+  var stmt = cps.DBConnection.createStatement(
+               "SELECT COUNT(*) AS count FROM settings " +
+               "WHERE id NOT IN (SELECT DISTINCT settingID FROM prefs)"
+             );
+  stmt.executeStep();
+  do_check_eq(0, stmt.row.count);
+  stmt.reset();
+  stmt.finalize();
+}