--- a/mfbt/AlreadyAddRefed.h
+++ b/mfbt/AlreadyAddRefed.h
@@ -22,16 +22,24 @@ struct unused_t;
 /**
  * already_AddRefed cooperates with reference counting smart pointers to enable
  * you to assign in a pointer _without_ |AddRef|ing it.  You might want to use
  * this as a return type from a function that returns an already |AddRef|ed
  * pointer.
  *
  * TODO Move already_AddRefed to namespace mozilla.  This has not yet been done
  * because of the sheer number of usages of already_AddRefed.
+ *
+ * When should you use already_AddRefed<>?
+ * * Ensure a consumer takes ownership of a reference
+ * * Pass ownership without calling AddRef/Release (sometimes required in
+ *   off-main-thread code)
+ * * The ref pointer type you're using doesn't support move construction
+ *
+ * Otherwise, use Move(RefPtr/nsCOMPtr/etc).
  */
 template<class T>
 struct MOZ_MUST_USE_TYPE MOZ_NON_AUTOABLE already_AddRefed
 {
   /*
    * We want to allow returning nullptr from functions returning
    * already_AddRefed<T>, for simplicity.  But we also don't want to allow
    * returning raw T*, instead preferring creation of already_AddRefed<T> from