--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -2902,17 +2902,16 @@ HTMLMediaElement::HTMLMediaElement(alrea
     mMediaSecurityVerified(false),
     mCORSMode(CORS_NONE),
     mIsEncrypted(false),
     mWaitingForKey(false),
     mDownloadSuspendedByCache(false, "HTMLMediaElement::mDownloadSuspendedByCache"),
     mAudioChannelVolume(1.0),
     mPlayingThroughTheAudioChannel(false),
     mDisableVideo(false),
-    mElementInTreeState(ELEMENT_NOT_INTREE),
     mHasUserInteraction(false),
     mFirstFrameLoaded(false),
     mDefaultPlaybackStartPosition(0.0),
     mIsAudioTrackAudible(false),
     mAudible(IsAudible()),
     mVisibilityState(Visibility::APPROXIMATELY_NONVISIBLE)
 {
   ErrorResult rv;
@@ -3403,25 +3402,27 @@ HTMLMediaElement::AfterSetAttr(int32_t a
 nsresult HTMLMediaElement::BindToTree(nsIDocument* aDocument, nsIContent* aParent,
                                       nsIContent* aBindingParent,
                                       bool aCompileEventHandlers)
 {
   nsresult rv = nsGenericHTMLElement::BindToTree(aDocument,
                                                  aParent,
                                                  aBindingParent,
                                                  aCompileEventHandlers);
+
+  mUnboundFromTree = false;
+
   if (aDocument) {
     mAutoplayEnabled =
       IsAutoplayEnabled() && (!aDocument || !aDocument->IsStaticDocument()) &&
       !IsEditable();
     // The preload action depends on the value of the autoplay attribute.
     // It's value may have changed, so update it.
     UpdatePreloadAction();
   }
-  mElementInTreeState = ELEMENT_INTREE;
 
   if (mDecoder) {
     // When the MediaElement is binding to tree, the dormant status is
     // aligned to document's hidden status.
     mDecoder->NotifyOwnerActivityChanged(!IsHidden());
   }
 
   return rv;
@@ -3645,22 +3646,22 @@ HTMLMediaElement::ReportTelemetry()
       }
     }
   }
 }
 
 void HTMLMediaElement::UnbindFromTree(bool aDeep,
                                       bool aNullParent)
 {
+  mUnboundFromTree = true;
+
   if (!mPaused && mNetworkState != nsIDOMHTMLMediaElement::NETWORK_EMPTY) {
     Pause();
   }
 
-  mElementInTreeState = ELEMENT_NOT_INTREE_HAD_INTREE;
-
   nsGenericHTMLElement::UnbindFromTree(aDeep, aNullParent);
 
   if (mDecoder) {
     MOZ_ASSERT(IsHidden());
     mDecoder->NotifyOwnerActivityChanged(false);
   }
 }
 
@@ -4984,21 +4985,18 @@ void HTMLMediaElement::CheckAutoplayData
 bool HTMLMediaElement::IsActive() const
 {
   nsIDocument* ownerDoc = OwnerDoc();
   return ownerDoc && ownerDoc->IsActive() && ownerDoc->IsVisible();
 }
 
 bool HTMLMediaElement::IsHidden() const
 {
-  if (mElementInTreeState == ELEMENT_NOT_INTREE_HAD_INTREE) {
-    return true;
-  }
-  nsIDocument* ownerDoc = OwnerDoc();
-  return !ownerDoc || ownerDoc->Hidden();
+  nsIDocument* ownerDoc;
+  return mUnboundFromTree || !(ownerDoc = OwnerDoc()) || ownerDoc->Hidden();
 }
 
 VideoFrameContainer* HTMLMediaElement::GetVideoFrameContainer()
 {
   if (mShuttingDown) {
     return nullptr;
   }
 

--- a/dom/html/HTMLMediaElement.h
+++ b/dom/html/HTMLMediaElement.h
@@ -1627,27 +1627,20 @@ protected:
   RefPtr<VideoTrackList> mVideoTrackList;
 
   nsAutoPtr<MediaStreamTrackListener> mMediaStreamTrackListener;
 
   // The principal guarding mVideoFrameContainer access when playing a
   // MediaStream.
   nsCOMPtr<nsIPrincipal> mSrcStreamVideoPrincipal;
 
-  enum ElementInTreeState {
-    // The MediaElement is not in the DOM tree now.
-    ELEMENT_NOT_INTREE,
-    // The MediaElement is in the DOM tree now.
-    ELEMENT_INTREE,
-    // The MediaElement is not in the DOM tree now but had been binded to the
-    // tree before.
-    ELEMENT_NOT_INTREE_HAD_INTREE
-  };
-
-  ElementInTreeState mElementInTreeState;
+  // True if UnbindFromTree() is called on the element.
+  // Note this flag is false when the element is in a phase after creation and
+  // before attaching to the DOM tree.
+  bool mUnboundFromTree = false;
 
 public:
   // Helper class to measure times for MSE telemetry stats
   class TimeDurationAccumulator
   {
   public:
     TimeDurationAccumulator()
       : mCount(0)