diff --git a/layout/style/CSSStyleSheet.h b/layout/style/CSSStyleSheet.h
index eefa301eb39..1a7798ed382 100644
--- a/layout/style/CSSStyleSheet.h
+++ b/layout/style/CSSStyleSheet.h
@@ -12,6 +12,7 @@
 #include "mozilla/Attributes.h"
 #include "mozilla/IncrementalClearCOMRuleArray.h"
 #include "mozilla/MemoryReporting.h"
+#include "mozilla/css/SheetParsingMode.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/CSSStyleSheetBinding.h"
 
@@ -51,35 +52,6 @@ namespace dom {
 class CSSRuleList;
 } // namespace dom
 
-namespace css {
-/**
- * Enum defining the mode in which a sheet is to be parsed.  This is
- * usually, but not always, the same as the cascade level at which the
- * sheet will apply (see nsStyleSet.h).  Most of the Loader APIs only
- * support loading of author sheets.
- *
- * Author sheets are the normal case: styles embedded in or linked
- * from HTML pages.  They are also the most restricted.
- *
- * User sheets can do anything author sheets can do, and also get
- * access to a few CSS extensions that are not yet suitable for
- * exposure on the public Web, but are very useful for expressing
- * user style overrides, such as @-moz-document rules.
- *
- * Agent sheets have access to all author- and user-sheet features
- * plus more extensions that are necessary for internal use but,
- * again, not yet suitable for exposure on the public Web.  Some of
- * these are outright unsafe to expose; in particular, incorrect
- * styling of anonymous box pseudo-elements can violate layout
- * invariants.
- */
-enum SheetParsingMode {
-  eAuthorSheetFeatures = 0,
-  eUserSheetFeatures,
-  eAgentSheetFeatures
-};
-}
-
   // -------------------------------
 // CSS Style Sheet Inner Data Container
 //
diff --git a/layout/style/SheetParsingMode.h b/layout/style/SheetParsingMode.h
new file mode 100644
index 00000000000..2eb6b2f64a6
--- /dev/null
+++ b/layout/style/SheetParsingMode.h
@@ -0,0 +1,43 @@
+/* -*- 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/. */
+
+#ifndef mozilla_css_SheetParsingMode_h
+#define mozilla_css_SheetParsingMode_h
+
+namespace mozilla {
+namespace css {
+
+/**
+ * Enum defining the mode in which a sheet is to be parsed.  This is
+ * usually, but not always, the same as the cascade level at which the
+ * sheet will apply (see nsStyleSet.h).  Most of the Loader APIs only
+ * support loading of author sheets.
+ *
+ * Author sheets are the normal case: styles embedded in or linked
+ * from HTML pages.  They are also the most restricted.
+ *
+ * User sheets can do anything author sheets can do, and also get
+ * access to a few CSS extensions that are not yet suitable for
+ * exposure on the public Web, but are very useful for expressing
+ * user style overrides, such as @-moz-document rules.
+ *
+ * Agent sheets have access to all author- and user-sheet features
+ * plus more extensions that are necessary for internal use but,
+ * again, not yet suitable for exposure on the public Web.  Some of
+ * these are outright unsafe to expose; in particular, incorrect
+ * styling of anonymous box pseudo-elements can violate layout
+ * invariants.
+ */
+enum SheetParsingMode {
+  eAuthorSheetFeatures = 0,
+  eUserSheetFeatures,
+  eAgentSheetFeatures
+};
+
+} // namespace css
+} // namespace mozilla
+
+#endif // mozilla_css_SheetParsingMode_h
diff --git a/layout/style/moz.build b/layout/style/moz.build
index 25095e1ad5b..1552bb30db8 100644
--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -116,6 +116,7 @@ EXPORTS.mozilla.css += [
     'Loader.h',
     'NameSpaceRule.h',
     'Rule.h',
+    'SheetParsingMode.h',
     'StyleRule.h',
 ]