--- a/dom/base/nsINode.h
+++ b/dom/base/nsINode.h
@@ -417,18 +417,16 @@ public:
     /** xml processing instructions */
     ePROCESSING_INSTRUCTION = 1 << 4,
     /** comment nodes */
     eCOMMENT             = 1 << 5,
     /** form control elements */
     eHTML_FORM_CONTROL   = 1 << 6,
     /** character data nodes (comments, PIs, text). */
     eDATA_NODE           = 1 << 8,
-    /** HTMLMediaElement */
-    eMEDIA               = 1 << 9,
     /** animation elements */
     eANIMATION           = 1 << 10,
     /** filter elements that implement SVGFilterPrimitiveStandardAttributes */
     eFILTER              = 1 << 11,
     /** SVGGeometryElement */
     eSHAPE               = 1 << 12
   };
 

--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -6518,22 +6518,16 @@ void HTMLMediaElement::DoRemoveSelfRefer
 
 void HTMLMediaElement::NotifyShutdownEvent()
 {
   mShuttingDown = true;
   ResetState();
   AddRemoveSelfReference();
 }
 
-bool
-HTMLMediaElement::IsNodeOfType(uint32_t aFlags) const
-{
-  return !(aFlags & ~eMEDIA);
-}
-
 void HTMLMediaElement::DispatchAsyncSourceError(nsIContent* aSourceElement)
 {
   LOG_EVENT(LogLevel::Debug, ("%p Queuing simple source error event", this));
 
   nsCOMPtr<nsIRunnable> event = new nsSourceErrorEventRunner(this, aSourceElement);
   mMainThreadEventTarget->Dispatch(event.forget());
 }
 

--- a/dom/html/HTMLMediaElement.h
+++ b/dom/html/HTMLMediaElement.h
@@ -373,18 +373,16 @@ public:
 
   /**
    * Called when a captured MediaStreamTrack is stopped so we can clean up its
    * MediaInputPort.
    */
   void NotifyOutputTrackStopped(DOMMediaStream* aOwningStream,
                                 TrackID aDestinationTrackID);
 
-  virtual bool IsNodeOfType(uint32_t aFlags) const override;
-
   /**
    * Returns the current load ID. Asynchronous events store the ID that was
    * current when they were enqueued, and if it has changed when they come to
    * fire, they consider themselves cancelled, and don't fire.
    */
   uint32_t GetCurrentLoadID() { return mCurrentLoadID; }
 
   /**

--- a/dom/html/HTMLSourceElement.cpp
+++ b/dom/html/HTMLSourceElement.cpp
@@ -3,16 +3,17 @@
 /* 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/HTMLSourceElement.h"
 #include "mozilla/dom/HTMLSourceElementBinding.h"
 
 #include "mozilla/dom/HTMLImageElement.h"
+#include "mozilla/dom/HTMLMediaElement.h"
 #include "mozilla/dom/ResponsiveImageSelector.h"
 #include "mozilla/dom/MediaList.h"
 #include "mozilla/dom/MediaSource.h"
 
 #include "nsGkAtoms.h"
 
 #include "nsHostObjectProtocolHandler.h"
 
@@ -147,18 +148,17 @@ HTMLSourceElement::BindToTree(nsIDocumen
                               bool aCompileEventHandlers)
 {
   nsresult rv = nsGenericHTMLElement::BindToTree(aDocument,
                                                  aParent,
                                                  aBindingParent,
                                                  aCompileEventHandlers);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  if (aParent && aParent->IsNodeOfType(nsINode::eMEDIA)) {
-    HTMLMediaElement* media = static_cast<HTMLMediaElement*>(aParent);
+  if (auto* media = HTMLMediaElement::FromNodeOrNull(aParent)) {
     media->NotifyAddedSource();
   }
 
   return NS_OK;
 }
 
 JSObject*
 HTMLSourceElement::WrapNode(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)

--- a/dom/html/HTMLTrackElement.cpp
+++ b/dom/html/HTMLTrackElement.cpp
@@ -356,23 +356,24 @@ HTMLTrackElement::BindToTree(nsIDocument
 {
   nsresult rv = nsGenericHTMLElement::BindToTree(aDocument,
                                                  aParent,
                                                  aBindingParent,
                                                  aCompileEventHandlers);
   NS_ENSURE_SUCCESS(rv, rv);
 
   LOG(LogLevel::Debug, ("Track Element bound to tree."));
-  if (!aParent || !aParent->IsNodeOfType(nsINode::eMEDIA)) {
+  auto* parent = HTMLMediaElement::FromNodeOrNull(aParent);
+  if (!parent) {
     return NS_OK;
   }
 
   // Store our parent so we can look up its frame for display.
   if (!mMediaParent) {
-    mMediaParent = static_cast<HTMLMediaElement*>(aParent);
+    mMediaParent = parent;
 
     // TODO: separate notification for 'alternate' tracks?
     mMediaParent->NotifyAddedSource();
     LOG(LogLevel::Debug, ("Track element sent notification to parent."));
 
     // We may already have a TextTrack at this point if GetTrack() has already
     // been called. This happens, for instance, if script tries to get the
     // TextTrack before its mTrackElement has been bound to the DOM tree.