diff --git a/toolkit/mozapps/update/updater/updater.cpp b/toolkit/mozapps/update/updater/updater.cpp
index 7d574fa064b..0a6402438cb 100644
--- a/toolkit/mozapps/update/updater/updater.cpp
+++ b/toolkit/mozapps/update/updater/updater.cpp
@@ -22,6 +22,13 @@
  *  be the first entry in the update manifest. The type is used to support
  *  downgrades by causing the actions defined in precomplete to be performed.
  *
+ *  updatev3.manifest
+ *  -----------------
+ *  method   = "add" | "add-if" | "add-if-not" | "patch" | "patch-if" |
+ *             "remove" | "rmdir" | "rmrfdir" | type
+ *
+ *  'add-if-not' adds a file if it doesn't exist.
+ *
  *  precomplete
  *  -----------
  *  method   = "remove" | "rmdir"
@@ -1580,6 +1587,67 @@ AddIfFile::Finish(int status)
   AddFile::Finish(status);
 }
 
+class AddIfNotFile : public AddFile
+{
+public:
+  AddIfNotFile() : mTestFile(NULL) { }
+
+  virtual int Parse(NS_tchar *line);
+  virtual int Prepare();
+  virtual int Execute();
+  virtual void Finish(int status);
+
+protected:
+  const NS_tchar *mTestFile;
+};
+
+int
+AddIfNotFile::Parse(NS_tchar *line)
+{
+  // format "<testfile>" "<newfile>"
+
+  mTestFile = get_valid_path(&line);
+  if (!mTestFile)
+    return PARSE_ERROR;
+
+  // consume whitespace between args
+  NS_tchar *q = mstrtok(kQuote, &line);
+  if (!q)
+    return PARSE_ERROR;
+
+  return AddFile::Parse(line);
+}
+
+int
+AddIfNotFile::Prepare()
+{
+  // If the test file exists, then skip this action.
+  if (!NS_taccess(mTestFile, F_OK)) {
+    mTestFile = NULL;
+    return OK;
+  }
+
+  return AddFile::Prepare();
+}
+
+int
+AddIfNotFile::Execute()
+{
+  if (!mTestFile)
+    return OK;
+
+  return AddFile::Execute();
+}
+
+void
+AddIfNotFile::Finish(int status)
+{
+  if (!mTestFile)
+    return;
+
+  AddFile::Finish(status);
+}
+
 class PatchIfFile : public PatchFile
 {
 public:
@@ -3624,9 +3692,9 @@ int DoUpdate()
   ensure_parent_dir(manifest);
 
   // extract the manifest
-  int rv = gArchiveReader.ExtractFile("updatev2.manifest", manifest);
+  int rv = gArchiveReader.ExtractFile("updatev3.manifest", manifest);
   if (rv) {
-    rv = gArchiveReader.ExtractFile("update.manifest", manifest);
+    rv = gArchiveReader.ExtractFile("updatev2.manifest", manifest);
     if (rv) {
       LOG(("DoUpdate: error extracting manifest file"));
       return rv;
@@ -3702,6 +3770,9 @@ int DoUpdate()
     else if (NS_tstrcmp(token, NS_T("add-if")) == 0) { // Add if exists
       action = new AddIfFile();
     }
+    else if (NS_tstrcmp(token, NS_T("add-if-not")) == 0) { // Add if not exists
+      action = new AddIfNotFile();
+    }
     else if (NS_tstrcmp(token, NS_T("patch-if")) == 0) { // Patch if exists
       action = new PatchIfFile();
     }