diff -r 000000000000 -r 6474c204b198 modules/libjar/zipwriter/test/unit/test_bug425768.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/libjar/zipwriter/test/unit/test_bug425768.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,31 @@
+/* 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/.
+ */
+
+const DIRNAME = "test/";
+const time = Date.now();
+
+function run_test()
+{
+  // Copy in the test file.
+  var source = do_get_file("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) + (ZIP_EXTENDED_TIMESTAMP_SIZE * 2);
+
+  do_check_eq(source.fileSize + extra, tmpFile.fileSize);
+}