Firefox isn't able to connect RDP Windows Server 2003

RDP with Firefox to legacy application on Windows Server 2003.

Message: The remote desktop server is currently unavailable. If the problem persists, please notify your system administrator, or check your system logs.

With Chrome it works.

With V1.0.0 it works with Firefox also.

Log Firefox:

09:13:22.001 [http-nio-8080-exec-7] INFO  o.a.g.tunnel.TunnelRequestService - User "admin" connected to connection "10".

Exception in thread "Thread-48" java.lang.IllegalStateException: Message will not be sent because the WebSocket session has been closed

    at org.apache.tomcat.websocket.WsRemoteEndpointImplBase.writeMessagePart(WsRemoteEndpointImplBase.java:449)

09:13:23.282 [http-nio-8080-exec-2] INFO  o.a.g.tunnel.TunnelRequestService - User "admin" disconnected from connection "10". Duration: 1278 milliseconds

    at org.apache.tomcat.websocket.WsRemoteEndpointImplBase.sendMessageBlock(WsRemoteEndpointImplBase.java:307)

    at org.apache.tomcat.websocket.WsRemoteEndpointImplBase.sendMessageBlock(WsRemoteEndpointImplBase.java:249)

    at org.apache.tomcat.websocket.WsRemoteEndpointImplBase.sendString(WsRemoteEndpointImplBase.java:191)

    at org.apache.tomcat.websocket.WsRemoteEndpointBasic.sendText(WsRemoteEndpointBasic.java:36)

    at org.apache.guacamole.websocket.GuacamoleWebSocketTunnelEndpoint.sendInstruction(GuacamoleWebSocketTunnelEndpoint.java:152)

    at org.apache.guacamole.websocket.GuacamoleWebSocketTunnelEndpoint.access$200(GuacamoleWebSocketTunnelEndpoint.java:53)

    at org.apache.guacamole.websocket.GuacamoleWebSocketTunnelEndpoint$2.run(GuacamoleWebSocketTunnelEndpoint.java:253)

Log Chrome:

09:15:43.364 [http-nio-8080-exec-7] INFO  o.a.g.r.auth.AuthenticationService - User "admin" successfully authenticated from [165.225.27.22, 172.21.31.3].

09:15:45.337 [http-nio-8080-exec-5] INFO  o.a.g.tunnel.TunnelRequestService - User "admin" connected to connection "10".