--- a/accessible/generic/FormControlAccessible.cpp
+++ b/accessible/generic/FormControlAccessible.cpp
@@ -4,17 +4,16 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 // NOTE: alphabetically ordered
 
 #include "FormControlAccessible.h"
 #include "Role.h"
 
 #include "mozilla/FloatingPoint.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "nsIDOMXULElement.h"
 #include "nsIDOMXULControlElement.h"
 
 using namespace mozilla::a11y;
 
 ////////////////////////////////////////////////////////////////////////////////
 // ProgressMeterAccessible
 ////////////////////////////////////////////////////////////////////////////////

--- a/dom/base/nsContentList.cpp
+++ b/dom/base/nsContentList.cpp
@@ -22,19 +22,16 @@
 #include "mozilla/dom/HTMLCollectionBinding.h"
 #include "mozilla/dom/NodeListBinding.h"
 #include "mozilla/Likely.h"
 #include "nsGenericHTMLElement.h"
 #include "jsfriendapi.h"
 #include <algorithm>
 #include "mozilla/dom/NodeInfoInlines.h"
 
-// Form related includes
-#include "nsIDOMHTMLFormElement.h"
-
 #include "PLDHashTable.h"
 
 #ifdef DEBUG_CONTENT_LIST
 #include "nsIContentIterator.h"
 #define ASSERT_IN_SYNC AssertInSync()
 #else
 #define ASSERT_IN_SYNC PR_BEGIN_MACRO PR_END_MACRO
 #endif

--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -129,17 +129,16 @@
 #include "nsIDocShell.h"
 #include "nsIDocShellTreeOwner.h"
 #include "nsIDocument.h"
 #include "nsIDocumentEncoder.h"
 #include "nsIDOMChromeWindow.h"
 #include "nsIDOMDocument.h"
 #include "nsIDOMDocumentType.h"
 #include "nsIDOMElement.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "nsIDOMNode.h"
 #include "nsIDOMNodeList.h"
 #include "nsIDOMWindowUtils.h"
 #include "nsIDragService.h"
 #include "nsIFormControl.h"
 #include "nsIForm.h"
 #include "nsIFragmentContentSink.h"
 #include "nsContainerFrame.h"

--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -120,17 +120,16 @@
 
 #include "nsBidiUtils.h"
 
 #include "nsContentCreatorFunctions.h"
 
 #include "nsIScriptContext.h"
 #include "nsBindingManager.h"
 #include "nsHTMLDocument.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "nsIRequest.h"
 #include "nsHostObjectProtocolHandler.h"
 
 #include "nsCharsetSource.h"
 #include "nsIParser.h"
 #include "nsIContentSink.h"
 
 #include "mozilla/EventDispatcher.h"
@@ -155,16 +154,17 @@
 #include "mozilla/dom/StyleRuleChangeEvent.h"
 #include "mozilla/dom/StyleSheetChangeEvent.h"
 #include "mozilla/dom/StyleSheetApplicableStateChangeEvent.h"
 #include "nsJSUtils.h"
 #include "nsFrameLoader.h"
 #include "nsEscape.h"
 #include "nsObjectLoadingContent.h"
 #include "nsHtml5TreeOpExecutor.h"
+#include "mozilla/dom/HTMLFormElement.h"
 #include "mozilla/dom/HTMLLinkElement.h"
 #include "mozilla/dom/HTMLMediaElement.h"
 #include "mozilla/dom/HTMLIFrameElement.h"
 #include "mozilla/dom/HTMLImageElement.h"
 #include "mozilla/dom/HTMLTextAreaElement.h"
 #include "mozilla/dom/MediaSource.h"
 
 #include "mozAutoDocUpdate.h"
@@ -8021,22 +8021,21 @@ nsDocument::Sanitize()
 
   // Now locate all _form_ elements that have autocomplete=off and reset them
   nodes = GetElementsByTagName(NS_LITERAL_STRING("form"));
 
   length = nodes->Length(true);
   for (uint32_t i = 0; i < length; ++i) {
     NS_ASSERTION(nodes->Item(i), "null item in nodelist");
 
-    nsCOMPtr<nsIDOMHTMLFormElement> form = do_QueryInterface(nodes->Item(i));
+    HTMLFormElement* form = HTMLFormElement::FromContent(nodes->Item(i));
     if (!form)
       continue;
 
-    nodes->Item(i)->AsElement()->GetAttr(kNameSpaceID_None,
-                                         nsGkAtoms::autocomplete, value);
+    form->GetAttr(kNameSpaceID_None, nsGkAtoms::autocomplete, value);
     if (value.LowerCaseEqualsLiteral("off"))
       form->Reset();
   }
 }
 
 void
 nsDocument::EnumerateSubDocuments(nsSubDocEnumFunc aCallback, void *aData)
 {

--- a/dom/html/HTMLButtonElement.cpp
+++ b/dom/html/HTMLButtonElement.cpp
@@ -4,17 +4,16 @@
  * 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 "mozilla/dom/HTMLButtonElement.h"
 
 #include "HTMLFormSubmissionConstants.h"
 #include "mozilla/dom/HTMLButtonElementBinding.h"
 #include "mozilla/dom/HTMLFormSubmission.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "nsAttrValueInlines.h"
 #include "nsGkAtoms.h"
 #include "nsIPresShell.h"
 #include "nsStyleConsts.h"
 #include "nsPresContext.h"
 #include "nsIFormControl.h"
 #include "nsIURL.h"
 #include "nsIFrame.h"

--- a/dom/html/HTMLFormElement.cpp
+++ b/dom/html/HTMLFormElement.cpp
@@ -160,18 +160,16 @@ NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHER
 void
 HTMLFormElement::AsyncEventRunning(AsyncEventDispatcher* aEvent)
 {
   if (mFormPasswordEventDispatcher == aEvent) {
     mFormPasswordEventDispatcher = nullptr;
   }
 }
 
-// nsIDOMHTMLFormElement
-
 NS_IMPL_ELEMENT_CLONE(HTMLFormElement)
 
 nsIHTMLCollection*
 HTMLFormElement::Elements()
 {
   return mControls;
 }
 
@@ -220,64 +218,51 @@ HTMLFormElement::AfterSetAttr(int32_t aN
       mControls->mNotInElements[i]->UpdateState(true);
     }
   }
 
   return nsGenericHTMLElement::AfterSetAttr(aNameSpaceID, aName, aValue,
                                             aOldValue, aSubjectPrincipal, aNotify);
 }
 
-NS_IMPL_STRING_ATTR(HTMLFormElement, AcceptCharset, acceptcharset)
-NS_IMPL_ACTION_ATTR(HTMLFormElement, Action, action)
-NS_IMPL_ENUM_ATTR_DEFAULT_VALUE(HTMLFormElement, Autocomplete, autocomplete,
-                                kFormDefaultAutocomplete->tag)
-NS_IMPL_ENUM_ATTR_DEFAULT_VALUE(HTMLFormElement, Enctype, enctype,
-                                kFormDefaultEnctype->tag)
-NS_IMPL_ENUM_ATTR_DEFAULT_VALUE(HTMLFormElement, Method, method,
-                                kFormDefaultMethod->tag)
-NS_IMPL_BOOL_ATTR(HTMLFormElement, NoValidate, novalidate)
-NS_IMPL_STRING_ATTR(HTMLFormElement, Name, name)
-NS_IMPL_STRING_ATTR(HTMLFormElement, Target, target)
+void HTMLFormElement::GetAutocomplete(nsAString& aValue)
+{
+  GetEnumAttr(nsGkAtoms::autocomplete, kFormDefaultAutocomplete->tag, aValue);
+}
+
+void HTMLFormElement::GetEnctype(nsAString& aValue)
+{
+  GetEnumAttr(nsGkAtoms::enctype, kFormDefaultEnctype->tag, aValue);
+}
+
+void HTMLFormElement::GetMethod(nsAString& aValue)
+{
+  GetEnumAttr(nsGkAtoms::method, kFormDefaultMethod->tag, aValue);
+}
 
 void
 HTMLFormElement::Submit(ErrorResult& aRv)
 {
   // Send the submit event
   if (mPendingSubmission) {
     // aha, we have a pending submission that was not flushed
     // (this happens when form.submit() is called twice)
     // we have to delete it and build a new one since values
     // might have changed inbetween (we emulate IE here, that's all)
     mPendingSubmission = nullptr;
   }
 
   aRv = DoSubmitOrReset(nullptr, eFormSubmit);
 }
 
-NS_IMETHODIMP
-HTMLFormElement::Submit()
-{
-  ErrorResult rv;
-  Submit(rv);
-  return rv.StealNSResult();
-}
-
-NS_IMETHODIMP
+void
 HTMLFormElement::Reset()
 {
   InternalFormEvent event(true, eFormReset);
   EventDispatcher::Dispatch(static_cast<nsIContent*>(this), nullptr, &event);
-  return NS_OK;
-}
-
-NS_IMETHODIMP
-HTMLFormElement::CheckValidity(bool* retVal)
-{
-  *retVal = CheckValidity();
-  return NS_OK;
 }
 
 bool
 HTMLFormElement::ParseAttribute(int32_t aNamespaceID,
                                 nsAtom* aAttribute,
                                 const nsAString& aValue,
                                 nsIPrincipal* aMaybeScriptedPrincipal,
                                 nsAttrValue& aResult)
@@ -1839,41 +1824,22 @@ HTMLFormElement::IsLastActiveElement(con
     if (element->IsSingleLineTextOrNumberControl(false) &&
         !element->IsDisabled()) {
       return element == aControl;
     }
   }
   return false;
 }
 
-NS_IMETHODIMP
-HTMLFormElement::GetEncoding(nsAString& aEncoding)
-{
-  return GetEnctype(aEncoding);
-}
-
-NS_IMETHODIMP
-HTMLFormElement::SetEncoding(const nsAString& aEncoding)
-{
-  return SetEnctype(aEncoding);
-}
-
 int32_t
 HTMLFormElement::Length()
 {
   return mControls->Length();
 }
 
-NS_IMETHODIMP
-HTMLFormElement::GetLength(int32_t* aLength)
-{
-  *aLength = Length();
-  return NS_OK;
-}
-
 void
 HTMLFormElement::ForgetCurrentSubmission()
 {
   mNotifiedObservers = false;
   mIsSubmitting = false;
   mSubmittingRequest = nullptr;
   nsCOMPtr<nsIWebProgress> webProgress = do_QueryReferent(mWebProgress);
   if (webProgress) {

--- a/dom/html/HTMLFormElement.h
+++ b/dom/html/HTMLFormElement.h
@@ -39,16 +39,18 @@ class HTMLFormElement final : public nsG
                               public nsIDOMHTMLFormElement,
                               public nsIWebProgressListener,
                               public nsIForm,
                               public nsIRadioGroupContainer
 {
   friend class HTMLFormControlsCollection;
 
 public:
+  NS_IMPL_FROMCONTENT_HTML_WITH_TAG(HTMLFormElement, form)
+
   explicit HTMLFormElement(already_AddRefed<mozilla::dom::NodeInfo>& aNodeInfo);
 
   enum {
     FORM_CONTROL_LIST_HASHTABLE_LENGTH = 8
   };
 
   // nsISupports
   NS_DECL_ISUPPORTS_INHERITED
@@ -320,41 +322,43 @@ public:
   }
 
   void SetAcceptCharset(const nsAString& aValue, ErrorResult& aRv)
   {
     SetHTMLAttr(nsGkAtoms::acceptcharset, aValue, aRv);
   }
 
   void GetAction(nsString& aValue);
-
   void SetAction(const nsAString& aValue, ErrorResult& aRv)
   {
     SetHTMLAttr(nsGkAtoms::action, aValue, aRv);
   }
 
-  // XPCOM GetAutocomplete() is OK
+  void GetAutocomplete(nsAString& aValue);
   void SetAutocomplete(const nsAString& aValue, ErrorResult& aRv)
   {
     SetHTMLAttr(nsGkAtoms::autocomplete, aValue, aRv);
   }
 
-  // XPCOM GetEnctype() is OK
+  void GetEnctype(nsAString& aValue);
   void SetEnctype(const nsAString& aValue, ErrorResult& aRv)
   {
     SetHTMLAttr(nsGkAtoms::enctype, aValue, aRv);
   }
 
-  // XPCOM GetEncoding() is OK
+  void GetEncoding(nsAString& aValue)
+  {
+    GetEnctype(aValue);
+  }
   void SetEncoding(const nsAString& aValue, ErrorResult& aRv)
   {
     SetEnctype(aValue, aRv);
   }
 
-  // XPCOM GetMethod() is OK
+  void GetMethod(nsAString& aValue);
   void SetMethod(const nsAString& aValue, ErrorResult& aRv)
   {
     SetHTMLAttr(nsGkAtoms::method, aValue, aRv);
   }
 
   void GetName(DOMString& aValue)
   {
     GetHTMLAttr(nsGkAtoms::name, aValue);
@@ -387,18 +391,17 @@ public:
 
   // it's only out-of-line because the class definition is not available in the
   // header
   nsIHTMLCollection* Elements();
 
   int32_t Length();
 
   void Submit(ErrorResult& aRv);
-
-  // XPCOM Reset() is OK
+  void Reset();
 
   bool CheckValidity()
   {
     return CheckFormValidity(nullptr);
   }
 
   bool ReportValidity()
   {

--- a/dom/html/HTMLFormSubmission.cpp
+++ b/dom/html/HTMLFormSubmission.cpp
@@ -7,17 +7,16 @@
 #include "HTMLFormSubmission.h"
 
 #include "nsCOMPtr.h"
 #include "nsIForm.h"
 #include "nsILinkHandler.h"
 #include "nsIDocument.h"
 #include "nsGkAtoms.h"
 #include "nsIFormControl.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "nsError.h"
 #include "nsGenericHTMLElement.h"
 #include "nsAttrValueInlines.h"
 #include "nsIFile.h"
 #include "nsDirectoryServiceDefs.h"
 #include "nsStringStream.h"
 #include "nsIURI.h"
 #include "nsIURL.h"

--- a/dom/html/HTMLInputElement.cpp
+++ b/dom/html/HTMLInputElement.cpp
@@ -29,17 +29,16 @@
 #include "nsIStringBundle.h"
 #include "nsFocusManager.h"
 #include "nsColorControlFrame.h"
 #include "nsNumberControlFrame.h"
 #include "nsPIDOMWindow.h"
 #include "nsRepeatService.h"
 #include "nsContentCID.h"
 #include "nsIComponentManager.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "mozilla/dom/ProgressEvent.h"
 #include "nsGkAtoms.h"
 #include "nsStyleConsts.h"
 #include "nsPresContext.h"
 #include "nsMappedAttributes.h"
 #include "nsIFormControl.h"
 #include "nsIDocument.h"
 #include "nsIPresShell.h"

--- a/dom/html/HTMLLegendElement.cpp
+++ b/dom/html/HTMLLegendElement.cpp
@@ -1,17 +1,16 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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 "mozilla/dom/HTMLLegendElement.h"
 #include "mozilla/dom/HTMLLegendElementBinding.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "nsFocusManager.h"
 #include "nsIFrame.h"
 
 NS_IMPL_NS_NEW_HTML_ELEMENT(Legend)
 
 namespace mozilla {
 namespace dom {
 

--- a/dom/html/HTMLOptionElement.cpp
+++ b/dom/html/HTMLOptionElement.cpp
@@ -2,17 +2,16 @@
 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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 "mozilla/dom/HTMLOptionElement.h"
 #include "mozilla/dom/HTMLOptionElementBinding.h"
 #include "mozilla/dom/HTMLSelectElement.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "nsGkAtoms.h"
 #include "nsStyleConsts.h"
 #include "nsIFormControl.h"
 #include "nsIForm.h"
 #include "nsIDOMNode.h"
 #include "nsISelectControlFrame.h"
 
 // Notify/query select frame for selected state

--- a/dom/html/HTMLTextAreaElement.cpp
+++ b/dom/html/HTMLTextAreaElement.cpp
@@ -19,17 +19,16 @@
 #include "nsContentCID.h"
 #include "nsContentCreatorFunctions.h"
 #include "nsError.h"
 #include "nsFocusManager.h"
 #include "nsIComponentManager.h"
 #include "nsIConstraintValidation.h"
 #include "nsIControllers.h"
 #include "nsIDocument.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "nsIFormControlFrame.h"
 #include "nsIFormControl.h"
 #include "nsIForm.h"
 #include "nsIFrame.h"
 #include "nsISupportsPrimitives.h"
 #include "nsITextControlFrame.h"
 #include "nsLayoutUtils.h"
 #include "nsLinebreakConverter.h"

--- a/dom/interfaces/html/nsIDOMHTMLFormElement.idl
+++ b/dom/interfaces/html/nsIDOMHTMLFormElement.idl
@@ -14,24 +14,9 @@
  *
  * with changes from the work-in-progress WHATWG HTML specification:
  * http://www.whatwg.org/specs/web-apps/current-work/
  */
 
 [uuid(ad9b2ad0-9d29-43f6-b1a2-a1fd24627e6b)]
 interface nsIDOMHTMLFormElement : nsISupports
 {
-           attribute DOMString            acceptCharset;
-           attribute DOMString            action;
-           attribute DOMString            autocomplete;
-           attribute DOMString            enctype;
-           attribute DOMString            encoding;
-           attribute DOMString            method;
-           attribute DOMString            name;
-           attribute boolean              noValidate;
-           attribute DOMString            target;
-
-  readonly attribute long                 length;
-
-  void                      submit();
-  void                      reset();
-  boolean                   checkValidity();
 };

--- a/dom/xul/nsXULContentSink.cpp
+++ b/dom/xul/nsXULContentSink.cpp
@@ -17,17 +17,16 @@
 #include "jsfriendapi.h"
 
 #include "nsCOMPtr.h"
 #include "nsForwardReference.h"
 #include "nsHTMLStyleSheet.h"
 #include "nsIContentSink.h"
 #include "nsIDocument.h"
 #include "nsIDOMEventListener.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "nsIFormControl.h"
 #include "mozilla/dom/NodeInfo.h"
 #include "nsIScriptContext.h"
 #include "nsIScriptGlobalObject.h"
 #include "nsIServiceManager.h"
 #include "nsIURL.h"
 #include "nsNameSpaceManager.h"
 #include "nsParserBase.h"

--- a/toolkit/components/satchel/nsFormFillController.cpp
+++ b/toolkit/components/satchel/nsFormFillController.cpp
@@ -28,17 +28,16 @@
 #include "nsPIDOMWindow.h"
 #include "nsIWebNavigation.h"
 #include "nsIContentViewer.h"
 #include "nsIDOMElement.h"
 #include "nsIDocument.h"
 #include "nsIContent.h"
 #include "nsIPresShell.h"
 #include "nsRect.h"
-#include "nsIDOMHTMLFormElement.h"
 #include "nsILoginManager.h"
 #include "nsIDOMMouseEvent.h"
 #include "mozilla/ModuleUtils.h"
 #include "nsToolkitCompsCID.h"
 #include "nsEmbedCID.h"
 #include "nsIDOMNSEditableElement.h"
 #include "nsContentUtils.h"
 #include "nsGenericHTMLElement.h"