--- a/content/base/src/nsFormData.cpp
+++ b/content/base/src/nsFormData.cpp
@@ -1,71 +1,68 @@
 /* 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/. */
 
 #include "nsFormData.h"
 #include "nsIVariant.h"
 #include "nsIInputStream.h"
 #include "nsIDOMFile.h"
-#include "nsContentUtils.h"
 #include "nsHTMLFormElement.h"
+#include "mozilla/dom/FormDataBinding.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
 
-nsFormData::nsFormData()
+nsFormData::nsFormData(nsISupports* aOwner)
   : nsFormSubmission(NS_LITERAL_CSTRING("UTF-8"), nullptr)
+  , mOwner(aOwner)
 {
+  SetIsDOMBinding();
 }
 
 // -------------------------------------------------------------------------
 // nsISupports
 
-DOMCI_DATA(FormData, nsFormData)
-
-NS_IMPL_ADDREF(nsFormData)
-NS_IMPL_RELEASE(nsFormData)
-NS_INTERFACE_MAP_BEGIN(nsFormData)
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_1(nsFormData, mOwner)
+NS_IMPL_CYCLE_COLLECTING_ADDREF(nsFormData)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(nsFormData)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsFormData)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
   NS_INTERFACE_MAP_ENTRY(nsIDOMFormData)
   NS_INTERFACE_MAP_ENTRY(nsIXHRSendable)
-  NS_INTERFACE_MAP_ENTRY(nsIJSNativeInitializer)
-  NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(FormData)
   NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIDOMFormData)
 NS_INTERFACE_MAP_END
 
 // -------------------------------------------------------------------------
 // nsFormSubmission
 nsresult
 nsFormData::GetEncodedSubmission(nsIURI* aURI,
                                  nsIInputStream** aPostDataStream)
 {
   NS_NOTREACHED("Shouldn't call nsFormData::GetEncodedSubmission");
   return NS_OK;
 }
 
-nsresult
-nsFormData::AddNameValuePair(const nsAString& aName,
-                             const nsAString& aValue)
+void
+nsFormData::Append(const nsAString& aName, const nsAString& aValue)
 {
   FormDataTuple* data = mFormData.AppendElement();
   data->name = aName;
   data->stringValue = aValue;
   data->valueIsFile = false;
-
-  return NS_OK;
 }
 
-nsresult
-nsFormData::AddNameFilePair(const nsAString& aName,
-                            nsIDOMBlob* aBlob)
+void
+nsFormData::Append(const nsAString& aName, nsIDOMBlob* aBlob)
 {
   FormDataTuple* data = mFormData.AppendElement();
   data->name = aName;
   data->fileValue = aBlob;
   data->valueIsFile = true;
-
-  return NS_OK;
 }
 
 // -------------------------------------------------------------------------
 // nsIDOMFormData
 
 NS_IMETHODIMP
 nsFormData::Append(const nsAString& aName, nsIVariant* aValue)
 {
@@ -79,29 +76,50 @@ nsFormData::Append(const nsAString& aNam
     nsID *iid;
     rv = aValue->GetAsInterface(&iid, getter_AddRefs(supports));
     NS_ENSURE_SUCCESS(rv, rv);
 
     nsMemory::Free(iid);
 
     nsCOMPtr<nsIDOMBlob> domBlob = do_QueryInterface(supports);
     if (domBlob) {
-      return AddNameFilePair(aName, domBlob);
+      Append(aName, domBlob);
+      return NS_OK;
     }
   }
 
   PRUnichar* stringData = nullptr;
   uint32_t stringLen = 0;
   rv = aValue->GetAsWStringWithSize(&stringLen, &stringData);
   NS_ENSURE_SUCCESS(rv, rv);
 
   nsString valAsString;
   valAsString.Adopt(stringData, stringLen);
 
-  return AddNameValuePair(aName, valAsString);
+  Append(aName, valAsString);
+  return NS_OK;
+}
+
+/* virtual */ JSObject*
+nsFormData::WrapObject(JSContext* aCx, JSObject* aScope, bool* aTriedToWrap)
+{
+  return FormDataBinding::Wrap(aCx, aScope, this, aTriedToWrap);
+}
+
+/* static */ already_AddRefed<nsFormData>
+nsFormData::Constructor(nsISupports* aGlobal,
+                        const Optional<nsHTMLFormElement*>& aFormElement,
+                        ErrorResult& aRv)
+{
+  nsRefPtr<nsFormData> formData = new nsFormData(aGlobal);
+  if (aFormElement.WasPassed()) {
+    MOZ_ASSERT(aFormElement.Value());
+    aRv = aFormElement.Value()->WalkFormElements(formData);
+  }
+  return formData.forget();
 }
 
 // -------------------------------------------------------------------------
 // nsIXHRSendable
 
 NS_IMETHODIMP
 nsFormData::GetSendInfo(nsIInputStream** aBody, uint64_t* aContentLength,
                         nsACString& aContentType, nsACString& aCharset)
@@ -119,40 +137,8 @@ nsFormData::GetSendInfo(nsIInputStream**
 
   fs.GetContentType(aContentType);
   aCharset.Truncate();
   *aContentLength = 0;
   NS_ADDREF(*aBody = fs.GetSubmissionBody(aContentLength));
 
   return NS_OK;
 }
-
-
-// -------------------------------------------------------------------------
-// nsIJSNativeInitializer
-
-NS_IMETHODIMP
-nsFormData::Initialize(nsISupports* aOwner,
-                       JSContext* aCx,
-                       JSObject* aObj,
-                       uint32_t aArgc,
-                       jsval* aArgv)
-{
-  if (aArgc > 0) {
-    if (JSVAL_IS_PRIMITIVE(aArgv[0])) {
-      return NS_ERROR_UNEXPECTED;
-    }
-    nsCOMPtr<nsIContent> formCont = do_QueryInterface(
-      nsContentUtils::XPConnect()->
-        GetNativeOfWrapper(aCx, JSVAL_TO_OBJECT(aArgv[0])));
-    
-    if (!formCont || !formCont->IsHTML(nsGkAtoms::form)) {
-      return NS_ERROR_UNEXPECTED;
-    }
-
-    nsresult rv = static_cast<nsHTMLFormElement*>(formCont.get())->
-      WalkFormElements(this);
-    NS_ENSURE_SUCCESS(rv, rv);
-  }
-
-
-  return NS_OK;
-}

--- a/content/base/src/nsFormData.h
+++ b/content/base/src/nsFormData.h
@@ -3,48 +3,86 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef nsFormData_h__
 #define nsFormData_h__
 
 #include "nsIDOMFormData.h"
 #include "nsIXMLHttpRequest.h"
 #include "nsFormSubmission.h"
-#include "nsIJSNativeInitializer.h"
+#include "nsWrapperCache.h"
 #include "nsTArray.h"
+#include "mozilla/ErrorResult.h"
 
+class nsHTMLFormElement;
 class nsIDOMFile;
 
+namespace mozilla {
+class ErrorResult;
+
+namespace dom {
+template<class> class Optional;
+} // namespace dom
+} // namespace mozilla
+
 class nsFormData : public nsIDOMFormData,
                    public nsIXHRSendable,
-                   public nsIJSNativeInitializer,
-                   public nsFormSubmission
+                   public nsFormSubmission,
+                   public nsWrapperCache
 {
 public:
-  nsFormData();
+  nsFormData(nsISupports* aOwner = nullptr);
 
-  NS_DECL_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(nsFormData,
+                                                         nsIDOMFormData)
+
   NS_DECL_NSIDOMFORMDATA
   NS_DECL_NSIXHRSENDABLE
 
+  // nsWrapperCache
+  virtual JSObject*
+  WrapObject(JSContext* aCx, JSObject* aScope, bool* aTriedToWrap) MOZ_OVERRIDE;
+
+  // WebIDL
+  nsISupports*
+  GetParentObject() const
+  {
+    return mOwner;
+  }
+  static already_AddRefed<nsFormData>
+  Constructor(nsISupports* aGlobal,
+              const mozilla::dom::Optional<nsHTMLFormElement*>& aFormElement,
+              mozilla::ErrorResult& aRv);
+  void Append(const nsAString& aName, const nsAString& aValue);
+  void Append(const nsAString& aName, nsIDOMBlob* aBlob);
+
   // nsFormSubmission
   virtual nsresult GetEncodedSubmission(nsIURI* aURI,
                                         nsIInputStream** aPostDataStream);
   virtual nsresult AddNameValuePair(const nsAString& aName,
-                                    const nsAString& aValue);
+                                    const nsAString& aValue)
+  {
+    Append(aName, aValue);
+    return NS_OK;
+  }
   virtual nsresult AddNameFilePair(const nsAString& aName,
-                                   nsIDOMBlob* aBlob);
+                                   nsIDOMBlob* aBlob)
+  {
+    Append(aName, aBlob);
+    return NS_OK;
+  }
 
-  NS_IMETHOD Initialize(nsISupports* aOwner, JSContext* aCx, JSObject* aObj,
-                        uint32_t aArgc, jsval* aArgv);
 private:
+  nsCOMPtr<nsISupports> mOwner;
+
   struct FormDataTuple
   {
     nsString name;
     nsString stringValue;
     nsCOMPtr<nsIDOMBlob> fileValue;
     bool valueIsFile;
   };
-  
+
   nsTArray<FormDataTuple> mFormData;
 };
 
 #endif // nsFormData_h__

--- a/content/base/src/nsXMLHttpRequest.cpp
+++ b/content/base/src/nsXMLHttpRequest.cpp
@@ -74,19 +74,20 @@
 #include "mozilla/dom/EncodingUtils.h"
 #include "mozilla/dom/XMLHttpRequestBinding.h"
 #include "nsIDOMFormData.h"
 #include "DictionaryHelpers.h"
 #include "mozilla/Attributes.h"
 #include "nsIPermissionManager.h"
 #include "nsMimeTypes.h"
 #include "nsIHttpChannelInternal.h"
+#include "nsFormData.h"
+#include "nsStreamListenerWrapper.h"
 
 #include "nsWrapperCacheInlines.h"
-#include "nsStreamListenerWrapper.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
 
 #define LOAD_STR "load"
 #define ERROR_STR "error"
 #define ABORT_STR "abort"
 #define TIMEOUT_STR "timeout"
@@ -2661,21 +2662,19 @@ nsXMLHttpRequest::GetRequestBody(nsIVari
     }
     case nsXMLHttpRequest::RequestBody::DOMString:
     {
       return ::GetRequestBody(*value.mString, aResult, aContentLength,
                               aContentType, aCharset);
     }
     case nsXMLHttpRequest::RequestBody::FormData:
     {
-      nsresult rv;
-      nsCOMPtr<nsIXHRSendable> sendable = do_QueryInterface(value.mFormData, &rv);
-      NS_ENSURE_SUCCESS(rv, rv);
-
-      return ::GetRequestBody(sendable, aResult, aContentLength, aContentType, aCharset);
+      MOZ_ASSERT(value.mFormData);
+      return ::GetRequestBody(value.mFormData, aResult, aContentLength,
+                              aContentType, aCharset);
     }
     case nsXMLHttpRequest::RequestBody::InputStream:
     {
       return ::GetRequestBody(value.mStream, aResult, aContentLength,
                               aContentType, aCharset);
     }
     default:
     {

--- a/content/base/src/nsXMLHttpRequest.h
+++ b/content/base/src/nsXMLHttpRequest.h
@@ -47,17 +47,17 @@
 /* Xlib headers insist on this for some reason... Nuke it because
    it'll override our member name */
 #undef Status
 #endif
 
 class nsILoadGroup;
 class AsyncVerifyRedirectCallbackForwarder;
 class nsIUnicodeDecoder;
-class nsIDOMFormData;
+class nsFormData;
 
 class nsXHREventTarget : public nsDOMEventTargetHelper,
                          public nsIXMLHttpRequestEventTarget
 {
 public:
   typedef mozilla::dom::XMLHttpRequestResponseType
           XMLHttpRequestResponseType;
   typedef mozilla::ErrorResult
@@ -283,19 +283,19 @@ private:
     RequestBody(nsIDocument* aDocument) : mType(Document)
     {
       mValue.mDocument = aDocument;
     }
     RequestBody(const nsAString& aString) : mType(DOMString)
     {
       mValue.mString = &aString;
     }
-    RequestBody(nsIDOMFormData* aFormData) : mType(FormData)
+    RequestBody(nsFormData& aFormData) : mType(FormData)
     {
-      mValue.mFormData = aFormData;
+      mValue.mFormData = &aFormData;
     }
     RequestBody(nsIInputStream* aStream) : mType(InputStream)
     {
       mValue.mStream = aStream;
     }
 
     enum Type {
       Uninitialized,
@@ -306,17 +306,17 @@ private:
       FormData,
       InputStream
     };
     union Value {
       mozilla::dom::ArrayBuffer* mArrayBuffer;
       nsIDOMBlob* mBlob;
       nsIDocument* mDocument;
       const nsAString* mString;
-      nsIDOMFormData* mFormData;
+      nsFormData* mFormData;
       nsIInputStream* mStream;
     };
 
     Type GetType() const
     {
       MOZ_ASSERT(mType != Uninitialized);
       return mType;
     }
@@ -371,19 +371,18 @@ public:
   {
     if (DOMStringIsNull(aString)) {
       Send(aRv);
     }
     else {
       aRv = Send(RequestBody(aString));
     }
   }
-  void Send(nsIDOMFormData* aFormData, ErrorResult& aRv)
+  void Send(nsFormData& aFormData, ErrorResult& aRv)
   {
-    NS_ASSERTION(aFormData, "Null should go to string version");
     aRv = Send(RequestBody(aFormData));
   }
   void Send(nsIInputStream* aStream, ErrorResult& aRv)
   {
     NS_ASSERTION(aStream, "Null should go to string version");
     aRv = Send(RequestBody(aStream));
   }
   void SendAsBinary(const nsAString& aBody, ErrorResult& aRv);

--- a/dom/base/nsDOMClassInfo.cpp
+++ b/dom/base/nsDOMClassInfo.cpp
@@ -422,17 +422,16 @@
 #include "nsIDOMNavigatorUserMedia.h"
 #endif
 
 // Workers
 #include "mozilla/dom/workers/Workers.h"
 
 #include "nsDOMFile.h"
 #include "nsDOMFileReader.h"
-#include "nsIDOMFormData.h"
 #include "ArchiveReader.h"
 #include "ArchiveRequest.h"
 
 #include "nsIDOMDesktopNotification.h"
 #include "nsIDOMNavigatorDesktopNotification.h"
 #include "nsIDOMNavigatorDeviceStorage.h"
 #include "nsIDOMNavigatorGeolocation.h"
 #include "Navigator.h"
@@ -1561,19 +1560,16 @@ static nsDOMClassInfoData sClassInfoData
   NS_DEFINE_CHROME_ONLY_CLASSINFO_DATA(ContentFrameMessageManager, nsEventTargetSH,
                                        DOM_DEFAULT_SCRIPTABLE_FLAGS |
                                        nsIXPCScriptable::IS_GLOBAL_OBJECT)
   NS_DEFINE_CHROME_ONLY_CLASSINFO_DATA(ChromeMessageBroadcaster, nsDOMGenericSH,
                                        DOM_DEFAULT_SCRIPTABLE_FLAGS)
   NS_DEFINE_CHROME_ONLY_CLASSINFO_DATA(ChromeMessageSender, nsDOMGenericSH,
                                        DOM_DEFAULT_SCRIPTABLE_FLAGS)
 
-  NS_DEFINE_CLASSINFO_DATA(FormData, nsDOMGenericSH,
-                           DOM_DEFAULT_SCRIPTABLE_FLAGS)
-
   NS_DEFINE_CLASSINFO_DATA(DesktopNotification, nsDOMGenericSH,
                            DOM_DEFAULT_SCRIPTABLE_FLAGS)
   NS_DEFINE_CLASSINFO_DATA(DesktopNotificationCenter, nsDOMGenericSH,
                            DOM_DEFAULT_SCRIPTABLE_FLAGS)
 
   NS_DEFINE_CLASSINFO_DATA(IDBFactory, IDBFactorySH,
                            DOM_DEFAULT_SCRIPTABLE_FLAGS)
   NS_DEFINE_CLASSINFO_DATA_WITH_NAME(IDBFileHandle, FileHandle, nsEventTargetSH,
@@ -1704,17 +1700,16 @@ static nsDOMClassInfoData sClassInfoData
     nsresult rv = NS_OK;                                                        \
     nsCOMPtr<nsISupports> native = do_CreateInstance(_contract_id, &rv);        \
     native.forget(aInstancePtrResult);                                          \
     return rv;                                                                  \
   }
 
 NS_DEFINE_CONTRACT_CTOR(FileReader, NS_FILEREADER_CONTRACTID)
 NS_DEFINE_CONTRACT_CTOR(ArchiveReader, NS_ARCHIVEREADER_CONTRACTID)
-NS_DEFINE_CONTRACT_CTOR(FormData, NS_FORMDATA_CONTRACTID)
 NS_DEFINE_CONTRACT_CTOR(XPathEvaluator, NS_XPATH_EVALUATOR_CONTRACTID)
 NS_DEFINE_CONTRACT_CTOR(XSLTProcessor,
                         "@mozilla.org/document-transformer;1?type=xslt")
 NS_DEFINE_CONTRACT_CTOR(EventSource, NS_EVENTSOURCE_CONTRACTID)
 NS_DEFINE_CONTRACT_CTOR(MutationObserver, NS_DOMMUTATIONOBSERVER_CONTRACTID)
 #ifdef MOZ_SYS_MSG
 NS_DEFINE_CONTRACT_CTOR(MozActivity, NS_DOMACTIVITY_CONTRACTID)
 #endif
@@ -1769,17 +1764,16 @@ static const nsConstructorFuncMapData kC
 #define MOZ_GENERATED_EVENT_LIST
 #define MOZ_GENERATED_EVENT(_event_interface) \
   NS_DEFINE_EVENT_CONSTRUCTOR_FUNC_DATA(_event_interface)
 #include "GeneratedEvents.h"
 #undef MOZ_GENERATED_EVENT_LIST
   NS_DEFINE_CONSTRUCTOR_FUNC_DATA(MozSmsFilter, sms::SmsFilter::NewSmsFilter)
   NS_DEFINE_CONSTRUCTOR_FUNC_DATA(FileReader, FileReaderCtor)
   NS_DEFINE_CONSTRUCTOR_FUNC_DATA(ArchiveReader, ArchiveReaderCtor)
-  NS_DEFINE_CONSTRUCTOR_FUNC_DATA(FormData, FormDataCtor)
   NS_DEFINE_CONSTRUCTOR_FUNC_DATA(XPathEvaluator, XPathEvaluatorCtor)
   NS_DEFINE_CONSTRUCTOR_FUNC_DATA(XSLTProcessor, XSLTProcessorCtor)
   NS_DEFINE_CONSTRUCTOR_FUNC_DATA(EventSource, EventSourceCtor)
   NS_DEFINE_CONSTRUCTOR_FUNC_DATA(MutationObserver, MutationObserverCtor)
 #ifdef MOZ_SYS_MSG
   NS_DEFINE_CONSTRUCTOR_FUNC_DATA(MozActivity, MozActivityCtor)
 #endif
 };
@@ -4196,20 +4190,16 @@ nsDOMClassInfo::Init()
 
   DOM_CLASSINFO_MAP_BEGIN_NO_CLASS_IF(ChromeMessageSender, nsISupports)
     DOM_CLASSINFO_MAP_ENTRY(nsIPermissionChecker)
     DOM_CLASSINFO_MAP_ENTRY(nsIFrameScriptLoader)
     DOM_CLASSINFO_MAP_ENTRY(nsIMessageListenerManager)
     DOM_CLASSINFO_MAP_ENTRY(nsIMessageSender)
   DOM_CLASSINFO_MAP_END
 
-  DOM_CLASSINFO_MAP_BEGIN(FormData, nsIDOMFormData)
-    DOM_CLASSINFO_MAP_ENTRY(nsIDOMFormData)
-  DOM_CLASSINFO_MAP_END
-
   DOM_CLASSINFO_MAP_BEGIN(DesktopNotification, nsIDOMDesktopNotification)
     DOM_CLASSINFO_MAP_ENTRY(nsIDOMDesktopNotification)
   DOM_CLASSINFO_MAP_END
 
   DOM_CLASSINFO_MAP_BEGIN(DesktopNotificationCenter, nsIDOMDesktopNotificationCenter)
     DOM_CLASSINFO_MAP_ENTRY(nsIDOMDesktopNotificationCenter)
   DOM_CLASSINFO_MAP_END
 

--- a/dom/base/nsDOMClassInfoClasses.h
+++ b/dom/base/nsDOMClassInfoClasses.h
@@ -443,18 +443,16 @@ DOMCI_CLASS(EventListenerInfo)
 
 DOMCI_CLASS(TransitionEvent)
 DOMCI_CLASS(AnimationEvent)
 
 DOMCI_CLASS(ContentFrameMessageManager)
 DOMCI_CLASS(ChromeMessageBroadcaster)
 DOMCI_CLASS(ChromeMessageSender)
 
-DOMCI_CLASS(FormData)
-
 DOMCI_CLASS(DesktopNotification)
 DOMCI_CLASS(DesktopNotificationCenter)
 
 DOMCI_CLASS(IDBFactory)
 DOMCI_CLASS(IDBFileHandle)
 DOMCI_CLASS(IDBRequest)
 DOMCI_CLASS(IDBDatabase)
 DOMCI_CLASS(IDBObjectStore)

--- a/dom/bindings/Bindings.conf
+++ b/dom/bindings/Bindings.conf
@@ -241,17 +241,22 @@ DOMInterfaces = {
 },
 
 'FileReaderSync': {
     'workers': True,
 },
 
 'FormData': [
 {
+    'nativeType': 'nsFormData'
+},
+{
     'workers': True,
+    'skipGen': True,
+    'nativeType': 'JSObject'
 }],
 
 'GainNode': [
 {
     'resultNotAddRefed': [ 'gain' ],
 }],
 
 'HTMLCollection': {
@@ -738,16 +743,17 @@ def addExternalIface(iface, nativeType=N
 # If you add one of these, you need to make sure nsDOMQS.h has the relevant
 # macros added for it
 def addExternalHTMLElement(element):
    nativeElement = 'ns' + element
    addExternalIface(element, nativeType=nativeElement,
                     headerFile=nativeElement + '.h')
 
 addExternalHTMLElement('HTMLCanvasElement')
+addExternalHTMLElement('HTMLFormElement')
 addExternalHTMLElement('HTMLImageElement')
 addExternalHTMLElement('HTMLMenuElement')
 addExternalHTMLElement('HTMLOptionElement')
 addExternalHTMLElement('HTMLOptGroupElement')
 addExternalHTMLElement('HTMLVideoElement')
 addExternalIface('Attr')
 addExternalIface('CanvasGradient', headerFile='nsIDOMCanvasRenderingContext2D.h')
 addExternalIface('CanvasPattern', headerFile='nsIDOMCanvasRenderingContext2D.h')

--- a/dom/imptests/failures/webapps/XMLHttpRequest/tests/submissions/Ms2ger/test_interfaces.html.json
+++ b/dom/imptests/failures/webapps/XMLHttpRequest/tests/submissions/Ms2ger/test_interfaces.html.json
@@ -1,15 +1,6 @@
 {
   "XMLHttpRequest interface constructor": true,
   "XMLHttpRequest interface: operation open(DOMString,DOMString,boolean,DOMString,DOMString)": true,
   "XMLHttpRequest interface: operation send(union)": true,
-  "FormData interface: existence and properties of interface object": true,
-  "FormData interface constructor": true,
-  "FormData interface: existence and properties of interface prototype object": true,
-  "FormData interface: existence and properties of interface prototype object's \"constructor\" property": true,
-  "Stringification of new FormData()": "debug",
-  "FormData interface: calling append(DOMString,Blob,DOMString) on new FormData() with too few arguments must throw TypeError": true,
-  "FormData interface: calling append(DOMString,DOMString) on new FormData() with too few arguments must throw TypeError": true,
-  "Stringification of new FormData(form)": "debug",
-  "FormData interface: calling append(DOMString,Blob,DOMString) on new FormData(form) with too few arguments must throw TypeError": true,
-  "FormData interface: calling append(DOMString,DOMString) on new FormData(form) with too few arguments must throw TypeError": true
+  "FormData interface constructor": true
 }

new file mode 100644
--- /dev/null
+++ b/dom/webidl/FormData.webidl
@@ -0,0 +1,18 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/.
+ *
+ * The origin of this IDL file is
+ * http://xhr.spec.whatwg.org
+ */
+
+interface HTMLFormElement;
+
+[Constructor(optional HTMLFormElement form)]
+interface FormData {
+  // Not supported (bug 739174)
+  // void append(DOMString name, Blob value, optional DOMString filename);
+  void append(DOMString name, Blob value);
+  void append(DOMString name, DOMString value);
+};

--- a/dom/webidl/WebIDL.mk
+++ b/dom/webidl/WebIDL.mk
@@ -31,16 +31,17 @@ webidl_files = \
   DynamicsCompressorNode.webidl \
   Element.webidl \
   EventHandler.webidl \
   EventListener.webidl \
   EventTarget.webidl \
   FileHandle.webidl \
   FileList.webidl \
   FileReaderSync.webidl \
+  FormData.webidl \
   Function.webidl \
   GainNode.webidl \
   HTMLCollection.webidl \
   HTMLElement.webidl \
   HTMLOptionsCollection.webidl \
   HTMLPropertiesCollection.webidl \
   ImageData.webidl \
   Node.webidl \

--- a/dom/webidl/XMLHttpRequest.webidl
+++ b/dom/webidl/XMLHttpRequest.webidl
@@ -7,17 +7,16 @@
  * www.w3.org/TR/2012/WD-XMLHttpRequest-20120117/
  *
  * Copyright © 2012 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C
  * liability, trademark and document use rules apply.
  */
 
 interface Document;
 interface Blob;
-interface FormData;
 interface InputStream;
 interface MozChannel;
 interface IID;
 
 enum XMLHttpRequestResponseType {
   "",
   "arraybuffer",
   "blob",

--- a/dom/workers/XMLHttpRequest.h
+++ b/dom/workers/XMLHttpRequest.h
@@ -174,16 +174,22 @@ public:
 
   void
   Send(const nsAString& aBody, ErrorResult& aRv);
 
   void
   Send(JSObject* aBody, ErrorResult& aRv);
 
   void
+  Send(JSObject& aBody, ErrorResult& aRv)
+  {
+    Send(&aBody, aRv);
+  }
+
+  void
   Send(ArrayBuffer& aBody, ErrorResult& aRv) {
     return Send(aBody.Obj(), aRv);
   }
 
   void
   SendAsBinary(const nsAString& aBody, ErrorResult& aRv);
 
   void

--- a/js/xpconnect/src/nsDOMQS.h
+++ b/js/xpconnect/src/nsDOMQS.h
@@ -4,16 +4,17 @@
 
 #ifndef nsDOMQS_h__
 #define nsDOMQS_h__
 
 #include "nsDOMClassInfoID.h"
 #include "nsGenericHTMLElement.h"
 #include "nsHTMLCanvasElement.h"
 #include "nsHTMLDivElement.h"
+#include "nsHTMLFormElement.h"
 #include "nsHTMLImageElement.h"
 #include "nsHTMLOptionElement.h"
 #include "nsHTMLOptGroupElement.h"
 #include "nsHTMLVideoElement.h"
 #include "nsHTMLDocument.h"
 #include "nsICSSDeclaration.h"
 #include "nsSVGStylableElement.h"
 
@@ -151,16 +152,17 @@ xpc_qsUnwrapArg<_clazz>(JSContext *cx, j
     nsISupports* argRef = static_cast<nsIContent*>(*ppArgRef);                \
     nsresult rv = xpc_qsUnwrapArg<_clazz>(cx, v, ppArg, &argRef, vp);         \
     *ppArgRef = static_cast<_clazz*>(static_cast<nsIContent*>(argRef));       \
     return rv;                                                                \
 }
 
 DEFINE_UNWRAP_CAST_HTML(canvas, nsHTMLCanvasElement)
 DEFINE_UNWRAP_CAST_HTML(div, nsHTMLDivElement)
+DEFINE_UNWRAP_CAST_HTML(form, nsHTMLFormElement)
 DEFINE_UNWRAP_CAST_HTML(img, nsHTMLImageElement)
 DEFINE_UNWRAP_CAST_HTML(optgroup, nsHTMLOptGroupElement)
 DEFINE_UNWRAP_CAST_HTML(option, nsHTMLOptionElement)
 DEFINE_UNWRAP_CAST_HTML(video, nsHTMLVideoElement)
 
 inline nsISupports*
 ToSupports(nsContentList *p)
 {