--- a/dom/media/MediaManager.cpp
+++ b/dom/media/MediaManager.cpp
@@ -2271,16 +2271,24 @@ MediaManager::GetUserMedia(nsPIDOMWindow
   }
 
   nsCOMPtr<nsIPrincipal> principal =
     nsGlobalWindowInner::Cast(aWindow)->GetPrincipal();
   if (NS_WARN_IF(!principal)) {
     return NS_ERROR_FAILURE;
   }
 
+  // Disallow access to null principal pages.
+  if (principal->GetIsNullPrincipal()) {
+    RefPtr<MediaStreamError> error =
+      new MediaStreamError(aWindow, NS_LITERAL_STRING("SecurityError"));
+    onFailure->OnError(error);
+    return NS_OK;
+  }
+
   // This principal needs to be sent to different threads and so via IPC.
   // For this reason it's better to convert it to PrincipalInfo right now.
   ipc::PrincipalInfo principalInfo;
   rv = PrincipalToPrincipalInfo(principal, &principalInfo);
   if (NS_WARN_IF(NS_FAILED(rv))) {
     return rv;
   }