--- a/docshell/base/nsDocShellTreeOwner.cpp
+++ b/docshell/base/nsDocShellTreeOwner.cpp
@@ -33,17 +33,16 @@
 #include "Link.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/SVGTitleElement.h"
 #include "nsIDOMEvent.h"
 #include "nsIDOMFileList.h"
 #include "nsIDOMMouseEvent.h"
 #include "nsIFormControl.h"
 #include "nsIDOMHTMLInputElement.h"
-#include "nsIDOMHTMLHtmlElement.h"
 #include "nsIDOMHTMLDocument.h"
 #include "nsIImageLoadingContent.h"
 #include "nsIWebNavigation.h"
 #include "nsIDOMHTMLElement.h"
 #include "nsIPresShell.h"
 #include "nsIStringBundle.h"
 #include "nsPIDOMWindow.h"
 #include "nsPIWindowRoot.h"

--- a/dom/html/HTMLSharedElement.cpp
+++ b/dom/html/HTMLSharedElement.cpp
@@ -26,72 +26,41 @@ namespace mozilla {
 namespace dom {
 
 extern nsAttrValue::EnumTable kListTypeTable[];
 
 HTMLSharedElement::~HTMLSharedElement()
 {
 }
 
-NS_IMPL_ADDREF_INHERITED(HTMLSharedElement, nsGenericHTMLElement)
-NS_IMPL_RELEASE_INHERITED(HTMLSharedElement, nsGenericHTMLElement)
-
-// QueryInterface implementation for HTMLSharedElement
-NS_INTERFACE_MAP_BEGIN(HTMLSharedElement)
-  NS_INTERFACE_MAP_ENTRY_IF_TAG(nsIDOMHTMLBaseElement, base)
-  NS_INTERFACE_MAP_ENTRY_IF_TAG(nsIDOMHTMLHtmlElement, html)
-NS_INTERFACE_MAP_END_INHERITING(nsGenericHTMLElement)
-
-
 NS_IMPL_ELEMENT_CLONE(HTMLSharedElement)
 
-// nsIDOMHTMLQuoteElement
-// Empty
-
-// nsIDOMHTMLHeadElement
-// Empty
-
-// nsIDOMHTMLHtmlElement
-NS_IMPL_STRING_ATTR(HTMLSharedElement, Version, version)
-
-// nsIDOMHTMLBaseElement
-NS_IMPL_STRING_ATTR(HTMLSharedElement, Target, target)
-
-NS_IMETHODIMP
+void
 HTMLSharedElement::GetHref(nsAString& aValue)
 {
   MOZ_ASSERT(mNodeInfo->Equals(nsGkAtoms::base),
              "This should only get called for <base> elements");
   nsAutoString href;
   GetAttr(kNameSpaceID_None, nsGkAtoms::href, href);
 
   nsCOMPtr<nsIURI> uri;
   nsIDocument* doc = OwnerDoc();
   nsContentUtils::NewURIWithDocumentCharset(
     getter_AddRefs(uri), href, doc, doc->GetFallbackBaseURI());
 
   if (!uri) {
     aValue = href;
-    return NS_OK;
+    return;
   }
 
   nsAutoCString spec;
   uri->GetSpec(spec);
   CopyUTF8toUTF16(spec, aValue);
-
-  return NS_OK;
 }
 
-NS_IMETHODIMP
-HTMLSharedElement::SetHref(const nsAString& aValue)
-{
-  return SetAttrHelper(nsGkAtoms::href, aValue);
-}
-
-
 bool
 HTMLSharedElement::ParseAttribute(int32_t aNamespaceID,
                                   nsAtom* aAttribute,
                                   const nsAString& aValue,
                                   nsAttrValue& aResult)
 {
   if (aNamespaceID == kNameSpaceID_None &&
       mNodeInfo->Equals(nsGkAtoms::dir)) {

--- a/dom/html/HTMLSharedElement.h
+++ b/dom/html/HTMLSharedElement.h
@@ -2,51 +2,38 @@
 /* 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/. */
 
 #ifndef mozilla_dom_HTMLSharedElement_h
 #define mozilla_dom_HTMLSharedElement_h
 
-#include "nsIDOMHTMLBaseElement.h"
-#include "nsIDOMHTMLHtmlElement.h"
 #include "nsGenericHTMLElement.h"
 
 #include "nsGkAtoms.h"
 
 #include "mozilla/Attributes.h"
 #include "mozilla/Assertions.h"
 
 namespace mozilla {
 namespace dom {
 
-class HTMLSharedElement final : public nsGenericHTMLElement,
-                                public nsIDOMHTMLBaseElement,
-                                public nsIDOMHTMLHtmlElement
+class HTMLSharedElement final : public nsGenericHTMLElement
 {
 public:
   explicit HTMLSharedElement(already_AddRefed<mozilla::dom::NodeInfo>& aNodeInfo)
     : nsGenericHTMLElement(aNodeInfo)
   {
     if (mNodeInfo->Equals(nsGkAtoms::head) ||
         mNodeInfo->Equals(nsGkAtoms::html)) {
       SetHasWeirdParserInsertionMode();
     }
   }
 
-  // nsISupports
-  NS_DECL_ISUPPORTS_INHERITED
-
-  // nsIDOMHTMLBaseElement
-  NS_DECL_NSIDOMHTMLBASEELEMENT
-
-  // nsIDOMHTMLHtmlElement
-  NS_DECL_NSIDOMHTMLHTMLELEMENT
-
   // nsIContent
   virtual bool ParseAttribute(int32_t aNamespaceID,
                                 nsAtom* aAttribute,
                                 const nsAString& aValue,
                                 nsAttrValue& aResult) override;
 
   virtual nsresult BindToTree(nsIDocument* aDocument, nsIContent* aParent,
                               nsIContent* aBindingParent,
@@ -110,17 +97,18 @@ public:
     MOZ_ASSERT(mNodeInfo->Equals(nsGkAtoms::base));
     GetHTMLAttr(nsGkAtoms::target, aValue);
   }
   void SetTarget(const nsAString& aValue, ErrorResult& aResult)
   {
     MOZ_ASSERT(mNodeInfo->Equals(nsGkAtoms::base));
     SetHTMLAttr(nsGkAtoms::target, aValue, aResult);
   }
-  // The XPCOM GetHref is fine for us
+
+  void GetHref(nsAString& aValue);
   void SetHref(const nsAString& aValue, ErrorResult& aResult)
   {
     MOZ_ASSERT(mNodeInfo->Equals(nsGkAtoms::base));
     SetHTMLAttr(nsGkAtoms::href, aValue, aResult);
   }
 
   // HTMLDirectoryElement
   bool Compact() const

--- a/dom/interfaces/html/moz.build
+++ b/dom/interfaces/html/moz.build
@@ -3,22 +3,20 @@
 # 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/.
 
 with Files("**"):
     BUG_COMPONENT = ("Core", "DOM")
 
 XPIDL_SOURCES += [
-    'nsIDOMHTMLBaseElement.idl',
     'nsIDOMHTMLCollection.idl',
     'nsIDOMHTMLDocument.idl',
     'nsIDOMHTMLElement.idl',
     'nsIDOMHTMLFormElement.idl',
-    'nsIDOMHTMLHtmlElement.idl',
     'nsIDOMHTMLInputElement.idl',
     'nsIDOMHTMLMediaElement.idl',
     'nsIDOMMozBrowserFrame.idl',
     'nsIDOMTimeRanges.idl',
     'nsIDOMValidityState.idl',
     'nsIMozBrowserFrame.idl',
 ]
 

deleted file mode 100644
--- a/dom/interfaces/html/nsIDOMHTMLBaseElement.idl
+++ /dev/null
@@ -1,24 +0,0 @@
-/* -*- 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/. */
-
-#include "nsIDOMHTMLElement.idl"
-
-/**
- * The nsIDOMHTMLBaseElement interface is the interface to a [X]HTML
- * base element.
- *
- * This interface is trying to follow the DOM Level 2 HTML specification:
- * http://www.w3.org/TR/DOM-Level-2-HTML/
- *
- * with changes from the work-in-progress WHATWG HTML specification:
- * http://www.whatwg.org/specs/web-apps/current-work/
- */
-
-[uuid(a348ac22-7880-4613-af4c-984ec2ef5adc)]
-interface nsIDOMHTMLBaseElement : nsISupports
-{
-           attribute DOMString        href;
-           attribute DOMString        target;
-};

deleted file mode 100644
--- a/dom/interfaces/html/nsIDOMHTMLHtmlElement.idl
+++ /dev/null
@@ -1,23 +0,0 @@
-/* -*- 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/. */
-
-#include "nsIDOMHTMLElement.idl"
-
-/**
- * The nsIDOMHTMLHtmlElement interface is the interface to a [X]HTML
- * html element.
- *
- * This interface is trying to follow the DOM Level 2 HTML specification:
- * http://www.w3.org/TR/DOM-Level-2-HTML/
- *
- * with changes from the work-in-progress WHATWG HTML specification:
- * http://www.whatwg.org/specs/web-apps/current-work/
- */
-
-[uuid(6a5d2ce7-2c45-43c1-bdab-9df7a06caed1)]
-interface nsIDOMHTMLHtmlElement : nsISupports
-{
-           attribute DOMString        version;
-};

--- a/dom/webbrowserpersist/WebBrowserPersistLocalDocument.cpp
+++ b/dom/webbrowserpersist/WebBrowserPersistLocalDocument.cpp
@@ -20,17 +20,16 @@
 #include "nsContentCID.h"
 #include "nsCycleCollectionParticipant.h"
 #include "nsFrameLoader.h"
 #include "nsIComponentRegistrar.h"
 #include "nsIContent.h"
 #include "nsIDOMAttr.h"
 #include "nsIDOMComment.h"
 #include "nsIDOMDocument.h"
-#include "nsIDOMHTMLBaseElement.h"
 #include "nsIDOMHTMLCollection.h"
 #include "nsIDOMHTMLDocument.h"
 #include "nsIDOMHTMLInputElement.h"
 #include "nsIDOMHTMLMediaElement.h"
 #include "nsIDOMMozNamedAttrMap.h"
 #include "nsIDOMNode.h"
 #include "nsIDOMNodeFilter.h"
 #include "nsIDOMNodeList.h"
@@ -894,45 +893,46 @@ PersistNodeFixup::FixupNode(nsIDOMNode *
                     FixupURI(href);
                     FixupXMLStyleSheetLink(outNode, href);
                 }
             }
         }
         return NS_OK;
     }
 
-    // BASE elements are replaced by a comment so relative links are not hosed.
-    if (!IsFlagSet(IWBP::PERSIST_FLAGS_NO_BASE_TAG_MODIFICATIONS)) {
-        nsCOMPtr<nsIDOMHTMLBaseElement> nodeAsBase = do_QueryInterface(aNodeIn);
-        if (nodeAsBase) {
-            nsCOMPtr<nsIDOMDocument> ownerDocument;
-            auto* base = static_cast<dom::HTMLSharedElement*>(nodeAsBase.get());
-            base->GetOwnerDocument(getter_AddRefs(ownerDocument));
-            if (ownerDocument) {
-                nsAutoString href;
-                base->GetHref(href); // Doesn't matter if this fails
-                nsCOMPtr<nsIDOMComment> comment;
-                nsAutoString commentText;
-                commentText.AssignLiteral(" base ");
-                if (!href.IsEmpty()) {
-                    commentText += NS_LITERAL_STRING("href=\"") + href
-                                   + NS_LITERAL_STRING("\" ");
-                }
-                rv = ownerDocument->CreateComment(commentText,
-                                                  getter_AddRefs(comment));
-                if (comment) {
-                    return CallQueryInterface(comment, aNodeOut);
-                }
-            }
-            return NS_OK;
-        }
+    nsCOMPtr<nsIContent> content = do_QueryInterface(aNodeIn);
+    if (!content) {
+        return NS_OK;
     }
 
-    nsCOMPtr<nsIContent> content = do_QueryInterface(aNodeIn);
-    if (!content) {
+    // BASE elements are replaced by a comment so relative links are not hosed.
+    if (!IsFlagSet(IWBP::PERSIST_FLAGS_NO_BASE_TAG_MODIFICATIONS) &&
+        content->IsHTMLElement(nsGkAtoms::base)) {
+        nsCOMPtr<nsIDOMDocument> ownerDocument;
+        // Base uses HTMLSharedElement, which would be awkward to implement
+        // FromContent on, since it represents multiple elements. Since we've
+        // already checked IsHTMLElement here, just cast as we were doing.
+        auto* base = static_cast<dom::HTMLSharedElement*>(content.get());
+        base->GetOwnerDocument(getter_AddRefs(ownerDocument));
+        if (ownerDocument) {
+            nsAutoString href;
+            base->GetHref(href); // Doesn't matter if this fails
+            nsCOMPtr<nsIDOMComment> comment;
+            nsAutoString commentText;
+            commentText.AssignLiteral(" base ");
+            if (!href.IsEmpty()) {
+                commentText += NS_LITERAL_STRING("href=\"") + href
+                    + NS_LITERAL_STRING("\" ");
+            }
+            rv = ownerDocument->CreateComment(commentText,
+                                              getter_AddRefs(comment));
+            if (comment) {
+                return CallQueryInterface(comment, aNodeOut);
+            }
+        }
         return NS_OK;
     }
 
     // Fix up href and file links in the elements
     RefPtr<dom::HTMLAnchorElement> nodeAsAnchor = dom::HTMLAnchorElement::FromContent(content);
     if (nodeAsAnchor) {
         rv = GetNodeToFixup(aNodeIn, aNodeOut);
         if (NS_SUCCEEDED(rv) && *aNodeOut) {

--- a/xpcom/reflect/xptinfo/ShimInterfaceInfo.cpp
+++ b/xpcom/reflect/xptinfo/ShimInterfaceInfo.cpp
@@ -40,22 +40,20 @@
 #include "nsIDOMElement.h"
 #include "nsIDOMEvent.h"
 #include "nsIDOMEventTarget.h"
 #include "nsIDOMFileList.h"
 #include "nsIDOMFocusEvent.h"
 #include "nsIDOMFormData.h"
 #include "nsIDOMGeoPositionError.h"
 #include "nsIDOMHistory.h"
-#include "nsIDOMHTMLBaseElement.h"
 #include "nsIDOMHTMLCollection.h"
 #include "nsIDOMHTMLDocument.h"
 #include "nsIDOMHTMLElement.h"
 #include "nsIDOMHTMLFormElement.h"
-#include "nsIDOMHTMLHtmlElement.h"
 #include "nsIDOMHTMLInputElement.h"
 #include "nsIDOMHTMLMediaElement.h"
 #include "nsIDOMKeyEvent.h"
 #include "nsIDOMMediaList.h"
 #include "nsIDOMMouseEvent.h"
 #include "nsIDOMMouseScrollEvent.h"
 #include "nsIDOMMutationEvent.h"
 #include "nsIDOMMozNamedAttrMap.h"
@@ -136,17 +134,16 @@
 #include "mozilla/dom/EventTargetBinding.h"
 #include "mozilla/dom/FileListBinding.h"
 #include "mozilla/dom/FocusEventBinding.h"
 #include "mozilla/dom/FormDataBinding.h"
 #include "mozilla/dom/FrameLoaderBinding.h"
 #include "mozilla/dom/HistoryBinding.h"
 #include "mozilla/dom/HTMLAnchorElementBinding.h"
 #include "mozilla/dom/HTMLAreaElementBinding.h"
-#include "mozilla/dom/HTMLBaseElementBinding.h"
 #include "mozilla/dom/HTMLButtonElementBinding.h"
 #include "mozilla/dom/HTMLCollectionBinding.h"
 #include "mozilla/dom/HTMLDocumentBinding.h"
 #include "mozilla/dom/HTMLElementBinding.h"
 #include "mozilla/dom/HTMLFormElementBinding.h"
 #include "mozilla/dom/HTMLFrameSetElementBinding.h"
 #include "mozilla/dom/HTMLHtmlElementBinding.h"
 #include "mozilla/dom/HTMLInputElementBinding.h"
@@ -288,22 +285,20 @@ const ComponentsInterfaceShimEntry kComp
   DEFINE_SHIM(Event),
   DEFINE_SHIM(EventTarget),
   DEFINE_SHIM(FileList),
   DEFINE_SHIM(FocusEvent),
   DEFINE_SHIM(FormData),
   DEFINE_SHIM_WITH_CUSTOM_INTERFACE(nsIFrameLoader, FrameLoader),
   DEFINE_SHIM_WITH_CUSTOM_INTERFACE(nsIDOMGeoPositionError, PositionError),
   DEFINE_SHIM(History),
-  DEFINE_SHIM(HTMLBaseElement),
   DEFINE_SHIM(HTMLCollection),
   DEFINE_SHIM(HTMLDocument),
   DEFINE_SHIM(HTMLElement),
   DEFINE_SHIM(HTMLFormElement),
-  DEFINE_SHIM(HTMLHtmlElement),
   DEFINE_SHIM(HTMLInputElement),
   DEFINE_SHIM(HTMLMediaElement),
   DEFINE_SHIM(KeyEvent),
   DEFINE_SHIM_WITH_CUSTOM_INTERFACE(nsIListBoxObject, ListBoxObject),
   DEFINE_SHIM(MediaList),
   DEFINE_SHIM_WITH_CUSTOM_INTERFACE(nsIMenuBoxObject, MenuBoxObject),
   DEFINE_SHIM(MouseEvent),
   DEFINE_SHIM(MouseScrollEvent),