diff -r 000000000000 -r 6474c204b198 xpcom/tests/unit/test_hidden_files.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/tests/unit/test_hidden_files.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,37 @@
+const Ci = Components.interfaces;
+const Cc = Components.classes;
+const NS_OS_TEMP_DIR = "TmpD";
+
+const CWD = do_get_cwd();
+function checkOS(os) {
+  const nsILocalFile_ = "nsILocalFile" + os;
+  return nsILocalFile_ in Components.interfaces &&
+         CWD instanceof Components.interfaces[nsILocalFile_];
+}
+
+const isWin = checkOS("Win");
+const isMac = checkOS("Mac");
+const isUnix = !(isWin || isMac);
+
+var hiddenUnixFile;
+function createUNIXHiddenFile() {
+  var dirSvc = Cc["@mozilla.org/file/directory_service;1"].getService(Ci.nsIProperties);
+  var tmpDir = dirSvc.get(NS_OS_TEMP_DIR, Ci.nsIFile);
+  hiddenUnixFile = tmpDir.clone();
+  hiddenUnixFile.append(".foo");
+  // we don't care if this already exists because we don't care
+  // about the file's contents (just the name)
+  if (!hiddenUnixFile.exists())
+    hiddenUnixFile.create(Ci.nsIFile.NORMAL_FILE_TYPE, 0666);
+  return hiddenUnixFile.exists();
+}
+
+function run_test() {
+  // Skip this test on Windows
+  if (isWin)
+    return;
+
+  do_check_true(createUNIXHiddenFile());
+  do_check_true(hiddenUnixFile.isHidden());
+}
+