diff --git a/xpcom/threads/nsIThreadPool.idl b/xpcom/threads/nsIThreadPool.idl
index c90ce200ef9..6a9b9977a93 100644
--- a/xpcom/threads/nsIThreadPool.idl
+++ b/xpcom/threads/nsIThreadPool.idl
@@ -36,6 +36,8 @@ interface nsIThreadPool : nsIEventTarget
    * thread (usually the thread that created this thread pool).  When this
    * function returns, the thread pool and all of its threads will be shutdown,
    * and it will no longer be possible to dispatch tasks to the thread pool.
+   *
+   * As a side effect, events on the current thread will be processed.
    */
   void shutdown();