diff -r 000000000000 -r 6474c204b198 modules/libjar/test/unit/test_bug379841.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/libjar/test/unit/test_bug379841.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,23 @@
+// Regression test for bug 379841 - nsIZipReader's last modified time ignores seconds
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const path = "data/test_bug379841.zip";
+// Retrieved time should be within 2 seconds of original file's time.
+const MAX_TIME_DIFF = 2000000;
+
+var ENTRY_NAME = "test";
+// Actual time of file was 07 May 2007 13:35:49 UTC
+var ENTRY_TIME = new Date(Date.UTC(2007, 4, 7, 13, 35, 49, 0));
+
+function run_test() {
+  var file = do_get_file(path);
+  var zipReader = Cc["@mozilla.org/libjar/zip-reader;1"].
+                  createInstance(Ci.nsIZipReader);
+  zipReader.open(file);
+  var entry = zipReader.getEntry(ENTRY_NAME);
+  var diff = Math.abs(entry.lastModifiedTime - ENTRY_TIME.getTime()*1000);
+  zipReader.close();
+  if (diff >= MAX_TIME_DIFF)
+    do_throw(diff);
+}