--- a/dom/fetch/InternalResponse.cpp
+++ b/dom/fetch/InternalResponse.cpp
@@ -127,16 +127,26 @@ InternalResponse::GetTainting() const
     case ResponseType::Opaque:
       return LoadTainting::Opaque;
     default:
       return LoadTainting::Basic;
   }
 }
 
 already_AddRefed<InternalResponse>
+InternalResponse::Unfiltered()
+{
+  RefPtr<InternalResponse> ref = mWrappedResponse;
+  if (!ref) {
+    ref = this;
+  }
+  return ref.forget();
+}
+
+already_AddRefed<InternalResponse>
 InternalResponse::OpaqueResponse()
 {
   MOZ_ASSERT(!mWrappedResponse, "Can't OpaqueResponse a already wrapped response");
   RefPtr<InternalResponse> response = new InternalResponse(0, EmptyCString());
   response->mType = ResponseType::Opaque;
   response->mTerminationReason = mTerminationReason;
   response->mChannelInfo = mChannelInfo;
   if (mPrincipalInfo) {

--- a/dom/fetch/InternalResponse.h
+++ b/dom/fetch/InternalResponse.h
@@ -216,16 +216,19 @@ public:
   SetPrincipalInfo(UniquePtr<mozilla::ipc::PrincipalInfo> aPrincipalInfo);
 
   nsresult
   StripFragmentAndSetUrl(const nsACString& aUrl);
 
   LoadTainting
   GetTainting() const;
 
+  already_AddRefed<InternalResponse>
+  Unfiltered();
+
 private:
   ~InternalResponse();
 
   explicit InternalResponse(const InternalResponse& aOther) = delete;
   InternalResponse& operator=(const InternalResponse&) = delete;
 
   // Returns an instance of InternalResponse which is a copy of this
   // InternalResponse, except headers, body and wrapped response (if any) which

--- a/dom/fetch/Response.cpp
+++ b/dom/fetch/Response.cpp
@@ -233,16 +233,30 @@ Response::Clone(ErrorResult& aRv) const
     return nullptr;
   }
 
   RefPtr<InternalResponse> ir = mInternalResponse->Clone();
   RefPtr<Response> response = new Response(mOwner, ir);
   return response.forget();
 }
 
+already_AddRefed<Response>
+Response::CloneUnfiltered(ErrorResult& aRv) const
+{
+  if (BodyUsed()) {
+    aRv.ThrowTypeError<MSG_FETCH_BODY_CONSUMED_ERROR>();
+    return nullptr;
+  }
+
+  RefPtr<InternalResponse> clone = mInternalResponse->Clone();
+  RefPtr<InternalResponse> ir = clone->Unfiltered();
+  RefPtr<Response> ref = new Response(mOwner, ir);
+  return ref.forget();
+}
+
 void
 Response::SetBody(nsIInputStream* aBody)
 {
   MOZ_ASSERT(!BodyUsed());
   mInternalResponse->SetBody(aBody);
 }
 
 already_AddRefed<InternalResponse>

--- a/dom/fetch/Response.h
+++ b/dom/fetch/Response.h
@@ -119,16 +119,19 @@ public:
   nsIGlobalObject* GetParentObject() const
   {
     return mOwner;
   }
 
   already_AddRefed<Response>
   Clone(ErrorResult& aRv) const;
 
+  already_AddRefed<Response>
+  CloneUnfiltered(ErrorResult& aRv) const;
+
   void
   SetBody(nsIInputStream* aBody);
 
   already_AddRefed<InternalResponse>
   GetInternalResponse() const;
 
 private:
   ~Response();

--- a/dom/webidl/Response.webidl
+++ b/dom/webidl/Response.webidl
@@ -19,16 +19,18 @@ interface Response {
   readonly attribute USVString url;
   readonly attribute unsigned short status;
   readonly attribute boolean ok;
   readonly attribute ByteString statusText;
   [SameObject] readonly attribute Headers headers;
 
   [Throws,
    NewObject] Response clone();
+
+  [ChromeOnly, NewObject, Throws] Response cloneUnfiltered();
 };
 Response implements Body;
 
 dictionary ResponseInit {
   unsigned short status = 200;
   // WebIDL spec doesn't allow default values for ByteString.
   ByteString statusText;
   HeadersInit headers;