--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -4662,17 +4662,17 @@ nsresult HTMLMediaElement::InitializeDec
     NS_ConvertUTF8toUTF16 mimeUTF16(mimeType);
     const char16_t* params[] = { mimeUTF16.get(), src.get() };
     ReportLoadError("MediaLoadUnsupportedMimeType", params, ArrayLength(params));
     return NS_ERROR_FAILURE;
   }
 
   LOG(LogLevel::Debug, ("%p Created decoder %p for type %s", this, decoder.get(), mimeType.get()));
 
-  bool isPrivateBrowsing = nsContentUtils::IsInPrivateBrowsing(OwnerDoc());
+  bool isPrivateBrowsing = NodePrincipal()->GetPrivateBrowsingId() > 0;
   RefPtr<MediaResource> resource = MediaResource::Create(
     decoder->GetResourceCallback(), aChannel, isPrivateBrowsing);
 
   if (!resource) {
     decoder->Shutdown();
     return NS_ERROR_OUT_OF_MEMORY;
   }