--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -3345,41 +3345,52 @@ HTMLMediaElement::AddCaptureMediaTrackTo
   }
 
   LOG(LogLevel::Debug,
       ("Created %s track %p with id %d from track %p through MediaInputPort %p",
        inputTrack->AsAudioStreamTrack() ? "audio" : "video",
        track.get(), destinationTrackID, inputTrack, port.get()));
 }
 
+bool
+HTMLMediaElement::CanBeCaptured(bool aCaptureAudio)
+{
+  // Don't bother capturing when the document has gone away
+  nsPIDOMWindowInner* window = OwnerDoc()->GetInnerWindow();
+  if (!window) {
+    return false;
+  }
+
+  // Prevent capturing restricted video
+  if (!aCaptureAudio && ContainsRestrictedContent()) {
+    return false;
+  }
+  return true;
+}
+
 already_AddRefed<DOMMediaStream>
 HTMLMediaElement::CaptureStreamInternal(bool aFinishWhenEnded,
                                         bool aCaptureAudio,
                                         MediaStreamGraph* aGraph)
 {
   MOZ_RELEASE_ASSERT(aGraph);
+  MOZ_ASSERT(CanBeCaptured(aCaptureAudio));
 
   MarkAsContentSource(CallerAPI::CAPTURE_STREAM);
   MarkAsTainted();
 
-  nsPIDOMWindowInner* window = OwnerDoc()->GetInnerWindow();
-  if (!window) {
-    return nullptr;
-  }
-  if (!aCaptureAudio && ContainsRestrictedContent()) {
-    return nullptr;
-  }
-
+  // We don't support routing to a different graph.
   if (!mOutputStreams.IsEmpty() &&
       aGraph != mOutputStreams[0].mStream->GetInputStream()->Graph()) {
     return nullptr;
   }
 
   OutputMediaStream* out = mOutputStreams.AppendElement();
   MediaStreamTrackSourceGetter* getter = new CaptureStreamTrackSourceGetter(this);
+  nsPIDOMWindowInner* window = OwnerDoc()->GetInnerWindow();
   out->mStream = DOMMediaStream::CreateTrackUnionStreamAsInput(window, aGraph, getter);
   out->mStream->SetInactiveOnFinish();
   out->mFinishWhenEnded = aFinishWhenEnded;
   out->mCapturingAudioOnly = aCaptureAudio;
 
   if (aCaptureAudio) {
     if (mSrcStream) {
       // We don't support applying volume and mute to the captured stream, when
@@ -3476,16 +3487,23 @@ HTMLMediaElement::CaptureAudio(ErrorResu
 }
 
 already_AddRefed<DOMMediaStream>
 HTMLMediaElement::MozCaptureStream(ErrorResult& aRv)
 {
   MediaStreamGraph::GraphDriverType graphDriverType =
     HasAudio() ? MediaStreamGraph::AUDIO_THREAD_DRIVER
                : MediaStreamGraph::SYSTEM_THREAD_DRIVER;
+
+
+  nsPIDOMWindowInner* window = OwnerDoc()->GetInnerWindow();
+  if (!window) {
+    return nullptr;
+  }
+
   MediaStreamGraph* graph =
     MediaStreamGraph::GetInstance(graphDriverType, mAudioChannel);
 
   RefPtr<DOMMediaStream> stream =
     CaptureStreamInternal(false, false, graph);
   if (!stream) {
     aRv.Throw(NS_ERROR_FAILURE);
     return nullptr;
@@ -3495,16 +3513,22 @@ HTMLMediaElement::MozCaptureStream(Error
 }
 
 already_AddRefed<DOMMediaStream>
 HTMLMediaElement::MozCaptureStreamUntilEnded(ErrorResult& aRv)
 {
   MediaStreamGraph::GraphDriverType graphDriverType =
     HasAudio() ? MediaStreamGraph::AUDIO_THREAD_DRIVER
                : MediaStreamGraph::SYSTEM_THREAD_DRIVER;
+
+  nsPIDOMWindowInner* window = OwnerDoc()->GetInnerWindow();
+  if (!window) {
+    return nullptr;
+  }
+
   MediaStreamGraph* graph =
     MediaStreamGraph::GetInstance(graphDriverType, mAudioChannel);
 
   RefPtr<DOMMediaStream> stream =
     CaptureStreamInternal(true, false, graph);
   if (!stream) {
     aRv.Throw(NS_ERROR_FAILURE);
     return nullptr;

--- a/dom/html/HTMLMediaElement.h
+++ b/dom/html/HTMLMediaElement.h
@@ -1274,16 +1274,19 @@ protected:
   bool IsAllowedToPlay();
 
   // If the network state is empty and then we would trigger DoLoad().
   void MaybeDoLoad();
 
   // Anything we need to check after played success and not related with spec.
   void UpdateCustomPolicyAfterPlayed();
 
+  // True if this element can be captured, false otherwise.
+  bool CanBeCaptured(bool aCaptureAudio);
+
   class nsAsyncEventRunner;
   class nsNotifyAboutPlayingRunner;
   class nsResolveOrRejectPendingPlayPromisesRunner;
   using nsGenericHTMLElement::DispatchEvent;
   // For nsAsyncEventRunner.
   nsresult DispatchEvent(const nsAString& aName);
 
   // Open unsupported types media with the external app when the media element