--- a/mfbt/Assertions.h
+++ b/mfbt/Assertions.h
@@ -33,16 +33,18 @@
  * use your version of this file under the terms of the MPL, indicate your
  * decision by deleting the provisions above and replace them with the notice
  * and other provisions required by the GPL or the LGPL. If you do not delete
  * the provisions above, a recipient may use your version of this file under
  * the terms of any one of the MPL, the GPL or the LGPL.
  *
  * ***** END LICENSE BLOCK ***** */
 
+/* Implementations of runtime and static assertion macros for C and C++. */
+
 #ifndef mozilla_Assertions_h_
 #define mozilla_Assertions_h_
 
 #include "mozilla/Types.h"
 
 /*
  * MOZ_STATIC_ASSERT may be used to assert a condition *at compile time*.  This
  * can be useful when you make certain assumptions about what must hold for

--- a/mfbt/RangedPtr.h
+++ b/mfbt/RangedPtr.h
@@ -33,16 +33,21 @@
  * use your version of this file under the terms of the MPL, indicate your
  * decision by deleting the provisions above and replace them with the notice
  * and other provisions required by the GPL or the LGPL. If you do not delete
  * the provisions above, a recipient may use your version of this file under
  * the terms of any one of the MPL, the GPL or the LGPL.
  *
  * ***** END LICENSE BLOCK ***** */
 
+/*
+ * Implements a smart pointer asserted to remain within a range specified at
+ * construction.
+ */
+
 #ifndef mozilla_RangedPtr_h_
 #define mozilla_RangedPtr_h_
 
 #include "mozilla/Assertions.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/Util.h"
 
 namespace mozilla {

--- a/mfbt/RefPtr.h
+++ b/mfbt/RefPtr.h
@@ -33,26 +33,24 @@
  * use your version of this file under the terms of the MPL, indicate your
  * decision by deleting the provisions above and replace them with the notice
  * and other provisions required by the GPL or the LGPL. If you do not delete
  * the provisions above, a recipient may use your version of this file under
  * the terms of any one of the MPL, the GPL or the LGPL.
  *
  * ***** END LICENSE BLOCK ***** */
 
+/* Helpers for defining and using refcounted objects. */
+
 #ifndef mozilla_RefPtr_h_
 #define mozilla_RefPtr_h_
 
 #include "mozilla/Assertions.h"
 #include "mozilla/Attributes.h"
 
-/**
- * Helpers for defining and using refcounted objects.
- */
-
 namespace mozilla {
 
 template<typename T> class RefCounted;
 template<typename T> class RefPtr;
 template<typename T> class TemporaryRef;
 template<typename T> class OutParamRef;
 template<typename T> OutParamRef<T> byRef(RefPtr<T>&);
 

--- a/mfbt/Util.h
+++ b/mfbt/Util.h
@@ -32,16 +32,21 @@
  * use your version of this file under the terms of the MPL, indicate your
  * decision by deleting the provisions above and replace them with the notice
  * and other provisions required by the GPL or the LGPL. If you do not delete
  * the provisions above, a recipient may use your version of this file under
  * the terms of any one of the MPL, the GPL or the LGPL.
  *
  * ***** END LICENSE BLOCK ***** */
 
+/*
+ * Miscellaneous uncategorized functionality.  Please add new functionality to
+ * new headers, or to other appropriate existing headers, not here.
+ */
+
 #ifndef mozilla_Util_h_
 #define mozilla_Util_h_
 
 #include "mozilla/Assertions.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/Types.h"
 
 #ifdef __cplusplus