--- a/layout/style/nsMediaList.cpp
+++ b/layout/style/nsMediaList.cpp
@@ -531,17 +531,17 @@ nsMediaList::Matches(nsPresContext* aPre
   for (int32_t i = 0, i_end = mArray.Length(); i < i_end; ++i) {
     if (mArray[i]->Matches(aPresContext, aKey)) {
       return true;
     }
   }
   return mArray.IsEmpty();
 }
 
-already_AddRefed<MediaList>
+already_AddRefed<dom::MediaList>
 nsMediaList::Clone()
 {
   RefPtr<nsMediaList> result = new nsMediaList();
   result->mArray.AppendElements(mArray.Length());
   for (uint32_t i = 0, i_end = mArray.Length(); i < i_end; ++i) {
     result->mArray[i] = mArray[i]->Clone();
     MOZ_ASSERT(result->mArray[i]);
   }