--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -4808,21 +4808,18 @@ nsDocument::SetScopeObject(nsIGlobalObje
       }
     }
   }
 }
 
 static void
 CheckIfContainsEMEContent(nsISupports* aSupports, void* aContainsEME)
 {
-  nsCOMPtr<nsIDOMHTMLMediaElement> domMediaElem(do_QueryInterface(aSupports));
-  if (domMediaElem) {
-    nsCOMPtr<nsIContent> content(do_QueryInterface(domMediaElem));
-    MOZ_ASSERT(content, "aSupports is not a content");
-    HTMLMediaElement* mediaElem = static_cast<HTMLMediaElement*>(content.get());
+  nsCOMPtr<nsIContent> content(do_QueryInterface(aSupports));
+  if (auto mediaElem = HTMLMediaElement::FromContentOrNull(content)) {
     bool* contains = static_cast<bool*>(aContainsEME);
     if (mediaElem->GetMediaKeys()) {
       *contains = true;
     }
   }
 }
 
 bool
@@ -4832,21 +4829,18 @@ nsDocument::ContainsEMEContent()
   EnumerateActivityObservers(CheckIfContainsEMEContent,
                              static_cast<void*>(&containsEME));
   return containsEME;
 }
 
 static void
 CheckIfContainsMSEContent(nsISupports* aSupports, void* aContainsMSE)
 {
-  nsCOMPtr<nsIDOMHTMLMediaElement> domMediaElem(do_QueryInterface(aSupports));
-  if (domMediaElem) {
-    nsCOMPtr<nsIContent> content(do_QueryInterface(domMediaElem));
-    MOZ_ASSERT(content, "aSupports is not a content");
-    HTMLMediaElement* mediaElem = static_cast<HTMLMediaElement*>(content.get());
+  nsCOMPtr<nsIContent> content(do_QueryInterface(aSupports));
+  if (auto mediaElem = HTMLMediaElement::FromContentOrNull(content)) {
     bool* contains = static_cast<bool*>(aContainsMSE);
     RefPtr<MediaSource> ms = mediaElem->GetMozMediaSourceObject();
     if (ms) {
       *contains = true;
     }
   }
 }
 
@@ -4857,21 +4851,18 @@ nsDocument::ContainsMSEContent()
   EnumerateActivityObservers(CheckIfContainsMSEContent,
                              static_cast<void*>(&containsMSE));
   return containsMSE;
 }
 
 static void
 NotifyActivityChanged(nsISupports *aSupports, void *aUnused)
 {
-  nsCOMPtr<nsIDOMHTMLMediaElement> domMediaElem(do_QueryInterface(aSupports));
-  if (domMediaElem) {
-    nsCOMPtr<nsIContent> content(do_QueryInterface(domMediaElem));
-    MOZ_ASSERT(content, "aSupports is not a content");
-    HTMLMediaElement* mediaElem = static_cast<HTMLMediaElement*>(content.get());
+  nsCOMPtr<nsIContent> content(do_QueryInterface(aSupports));
+  if (auto mediaElem = HTMLMediaElement::FromContentOrNull(content)) {
     mediaElem->NotifyOwnerDocumentActivityChanged();
   }
   nsCOMPtr<nsIObjectLoadingContent> objectLoadingContent(do_QueryInterface(aSupports));
   if (objectLoadingContent) {
     nsObjectLoadingContent* olc = static_cast<nsObjectLoadingContent*>(objectLoadingContent.get());
     olc->NotifyOwnerDocumentActivityChanged();
   }
   nsCOMPtr<nsIDocumentActivity> objectDocumentActivity(do_QueryInterface(aSupports));

--- a/dom/base/nsNodeUtils.cpp
+++ b/dom/base/nsNodeUtils.cpp
@@ -600,19 +600,18 @@ nsNodeUtils::CloneAndAdopt(nsINode *aNod
           if (elm->MayHaveSelectionChangeEventListener()) {
             window->SetHasSelectionChangeEventListeners();
           }
         }
       }
     }
 
     if (wasRegistered && oldDoc != newDoc) {
-      nsCOMPtr<nsIDOMHTMLMediaElement> domMediaElem(do_QueryInterface(aNode));
-      if (domMediaElem) {
-        HTMLMediaElement* mediaElem = static_cast<HTMLMediaElement*>(aNode);
+      nsIContent* content = aNode->AsContent();
+      if (auto mediaElem = HTMLMediaElement::FromContentOrNull(content)) {
         mediaElem->NotifyOwnerDocumentActivityChanged();
       }
       nsCOMPtr<nsIObjectLoadingContent> objectLoadingContent(do_QueryInterface(aNode));
       if (objectLoadingContent) {
         nsObjectLoadingContent* olc = static_cast<nsObjectLoadingContent*>(objectLoadingContent.get());
         olc->NotifyOwnerDocumentActivityChanged();
       }
     }

--- a/dom/html/HTMLAudioElement.h
+++ b/dom/html/HTMLAudioElement.h
@@ -16,16 +16,18 @@ typedef uint16_t nsMediaReadyState;
 namespace mozilla {
 namespace dom {
 
 class HTMLAudioElement final : public HTMLMediaElement
 {
 public:
   typedef mozilla::dom::NodeInfo NodeInfo;
 
+  NS_IMPL_FROMCONTENT_HTML_WITH_TAG(HTMLAudioElement, audio)
+
   explicit HTMLAudioElement(already_AddRefed<NodeInfo>& aNodeInfo);
 
   // Element
   virtual bool IsInteractiveHTMLContent(bool aIgnoreTabindex) const override;
 
   // nsIDOMHTMLMediaElement
   using HTMLMediaElement::GetPaused;
 

--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -2,16 +2,18 @@
 /* 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/HTMLMediaElement.h"
 #include "mozilla/dom/HTMLMediaElementBinding.h"
 #include "mozilla/dom/HTMLSourceElement.h"
+#include "mozilla/dom/HTMLAudioElement.h"
+#include "mozilla/dom/HTMLVideoElement.h"
 #include "mozilla/dom/ElementInlines.h"
 #include "mozilla/dom/Promise.h"
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/NotNull.h"
 #include "mozilla/MathAlgorithms.h"
 #include "mozilla/AsyncEventDispatcher.h"
 #include "mozilla/dom/MediaEncryptedEvent.h"
 #include "mozilla/EMEUtils.h"

--- a/dom/html/HTMLMediaElement.h
+++ b/dom/html/HTMLMediaElement.h
@@ -139,16 +139,19 @@ public:
 
   // nsIDOMHTMLMediaElement
   NS_DECL_NSIDOMHTMLMEDIAELEMENT
 
   // nsISupports
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(HTMLMediaElement,
                                            nsGenericHTMLElement)
+  NS_IMPL_FROMCONTENT_HELPER(HTMLMediaElement,
+                             IsAnyOfHTMLElements(nsGkAtoms::video,
+                                                 nsGkAtoms::audio))
 
   // nsIDOMEventTarget
   virtual nsresult
   GetEventTargetParent(EventChainPreVisitor& aVisitor) override;
 
   virtual bool ParseAttribute(int32_t aNamespaceID,
                               nsAtom* aAttribute,
                               const nsAString& aValue,

--- a/layout/generic/nsVideoFrame.cpp
+++ b/layout/generic/nsVideoFrame.cpp
@@ -804,43 +804,38 @@ nsVideoFrame::AttributeChanged(int32_t a
                                             aModType);
 }
 
 void
 nsVideoFrame::OnVisibilityChange(Visibility aNewVisibility,
                                  const Maybe<OnNonvisible>& aNonvisibleAction)
 {
   if (HasVideoElement()) {
-    nsCOMPtr<nsIDOMHTMLMediaElement> mediaDomElement = do_QueryInterface(mContent);
-    mediaDomElement->OnVisibilityChange(aNewVisibility);
+    static_cast<HTMLMediaElement*>(mContent)->OnVisibilityChange(aNewVisibility);
   }
 
   nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(mPosterImage);
   if (imageLoader) {
     imageLoader->OnVisibilityChange(aNewVisibility,
                                     aNonvisibleAction);
   }
 
   nsContainerFrame::OnVisibilityChange(aNewVisibility, aNonvisibleAction);
 }
 
 bool nsVideoFrame::HasVideoElement() {
-  nsCOMPtr<nsIDOMHTMLMediaElement> mediaDomElement = do_QueryInterface(mContent);
-  return mediaDomElement->IsVideo();
+  return static_cast<HTMLMediaElement*>(mContent)->IsVideo();
 }
 
 bool nsVideoFrame::HasVideoData()
 {
   if (!HasVideoElement())
     return false;
   HTMLVideoElement* element = static_cast<HTMLVideoElement*>(GetContent());
   nsIntSize size(0, 0);
   element->GetVideoSize(&size);
   return size != nsIntSize(0,0);
 }
 
 void nsVideoFrame::UpdateTextTrack()
 {
-  HTMLMediaElement* element = static_cast<HTMLMediaElement*>(GetContent());
-  if (element) {
-    element->NotifyCueDisplayStatesChanged();
-  }
+  static_cast<HTMLMediaElement*>(mContent)->NotifyCueDisplayStatesChanged();
 }