diff -r 000000000000 -r 6474c204b198 modules/libjar/zipwriter/test/unit/test_zipcomment.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/libjar/zipwriter/test/unit/test_zipcomment.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,34 @@
+/* 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 DATA = "ZIP WRITER TEST COMMENT";
+const DATA2 = "ANOTHER ONE";
+
+function run_test()
+{
+  zipW.open(tmpFile, PR_RDWR | PR_CREATE_FILE | PR_TRUNCATE);
+  zipW.comment = DATA;
+  zipW.close();
+
+  // Should have created a zip file
+  do_check_true(tmpFile.exists());
+
+  // Empty zip file should just be the end of central directory marker
+  // and comment
+  do_check_eq(tmpFile.fileSize, ZIP_EOCDR_HEADER_SIZE + DATA.length);
+
+  zipW.open(tmpFile, PR_RDWR);
+  // Should have the set comment
+  do_check_eq(zipW.comment, DATA);
+  zipW.comment = DATA2;
+  zipW.close();
+
+  // Certain platforms cache the file size so get a fresh file to check.
+  tmpFile = tmpFile.clone();
+
+  // Empty zip file should just be the end of central directory marker
+  // and comment. This should now be shorter
+  do_check_eq(tmpFile.fileSize, ZIP_EOCDR_HEADER_SIZE + DATA2.length);
+}