diff --git a/mozilla/modules/libjar/zipwriter/test/unit/test_bug425768.js b/mozilla/modules/libjar/zipwriter/test/unit/test_bug425768.js
new file mode 100644
index 00000000000..f10e4599cd9
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+++ b/mozilla/modules/libjar/zipwriter/test/unit/test_bug425768.js
@@ -0,0 +1,62 @@
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is Zip Writer Component.
+ *
+ * The Initial Developer of the Original Code is
+ * Dave Townsend <dtownsend@oxymoronical.com>.
+ *
+ * Portions created by the Initial Developer are Copyright (C) 2008
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK *****
+ */
+
+const DIRNAME = "test/";
+const time = Date.now();
+
+function run_test()
+{
+  // Copy in the test file.
+  var source = do_get_file("modules/libjar/zipwriter/test/unit/data/test.zip");
+  source.copyTo(tmpFile.parent, tmpFile.leafName);
+
+  // Open it and add something so the CDS is rewritten.
+  zipW.open(tmpFile, PR_RDWR | PR_APPEND);
+  zipW.addEntryDirectory(DIRNAME, time * PR_USEC_PER_MSEC, false);
+  do_check_true(zipW.hasEntry(DIRNAME));
+  zipW.close();
+
+  var zipR = new ZipReader(tmpFile);
+  do_check_true(zipR.hasEntry(DIRNAME));
+  zipR.close();
+
+  // Adding the directory would have added a fixed amount to the file size.
+  // Any difference suggests the CDS was written out incorrectly.
+  var extra = ZIP_FILE_HEADER_SIZE + ZIP_CDS_HEADER_SIZE + (DIRNAME.length * 2);
+  do_check_eq(source.fileSize + extra, tmpFile.fileSize);
+}