Firefox Javascript WebSockets close call blocked

I am using javascript to init a websocket to a Tomcat server end point. For most cases, this works fine. The socket would close and open with client receiving and receiving the expected close event.

However, in one case, the client close would not send the close event to the server when calling the socket close. Thus, delaying server side close (abnormal close (The connection was closed abnormally, e.g., without sending or receiving a Close control frame) 1006 error on final close timeout). Is there a way to debug in the browser as to why the close event hanged? This is for firefox. Similarly, although I do not see the close call in chrome websocket packet sniffer.. it would be nice to know if there are some scenarios where tomcat would hang this call upon receiving it.