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diff --git a/xpcom/base/nsVersionComparator.h b/xpcom/base/nsVersionComparator.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+// NB: This code may be used from non-XPCOM code, in particular, the
+// standalone updater executable.
+
+#ifndef nsVersionComparator_h__
+#define nsVersionComparator_h__
+
+#include "mozilla/Char16.h"
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#if defined(XP_WIN) && !defined(UPDATER_NO_STRING_GLUE_STL)
+#  include <wchar.h>
+#  include "nsString.h"
+#endif
+
+/**
+ * In order to compare version numbers in Mozilla, you need to use the
+ * mozilla::Version class.  You can construct an object of this type by passing
+ * in a string version number to the constructor.  Objects of this type can be
+ * compared using the standard comparison operators.
+ *
+ * For example, let's say that you want to make sure that a given version
+ * number is not older than 15.a2.  Here's how you would write a function to
+ * do that.
+ *
+ * bool IsVersionValid(const char* version) {
+ *   return mozilla::Version("15.a2") <= mozilla::Version(version);
+ * }
+ *
+ * Or, since Version's constructor is implicit, you can simplify this code:
+ *
+ * bool IsVersionValid(const char* version) {
+ *   return mozilla::Version("15.a2") <= version;
+ * }
+ */
+
+namespace mozilla {
+
+/**
+ * Compares the version strings provided.
+ *
+ * Returns 0 if the versions match, < 0 if aStrB > aStrA and > 0 if
+ * aStrA > aStrB.
+ */
+int32_t CompareVersions(const char* aStrA, const char* aStrB);
+
+#ifdef XP_WIN
+/**
+ * As above but for wide character strings.
+ */
+int32_t CompareVersions(const char16_t* aStrA, const char16_t* aStrB);
+#endif
+
+struct Version {
+  explicit Version(const char* aVersionString) {
+    versionContent = strdup(aVersionString);
+  }
+
+  const char* ReadContent() const { return versionContent; }
+
+  ~Version() { free(versionContent); }
+
+  bool operator<(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) < 0;
+  }
+  bool operator<=(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) < 1;
+  }
+  bool operator>(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) > 0;
+  }
+  bool operator>=(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) > -1;
+  }
+  bool operator==(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) == 0;
+  }
+  bool operator!=(const Version& aRhs) const {
+    return CompareVersions(versionContent, aRhs.ReadContent()) != 0;
+  }
+  bool operator<(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) < 0;
+  }
+  bool operator<=(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) < 1;
+  }
+  bool operator>(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) > 0;
+  }
+  bool operator>=(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) > -1;
+  }
+  bool operator==(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) == 0;
+  }
+  bool operator!=(const char* aRhs) const {
+    return CompareVersions(versionContent, aRhs) != 0;
+  }
+
+ private:
+  char* versionContent;
+};
+
+}  // namespace mozilla
+
+#endif  // nsVersionComparator_h__