win7 Ent running FireFox 22.0 sends the FIN after 6 secs completing the TCP 3-way handshake

hello Product experts!

win7 Ent  running FireFox 22.0 sends the FIN after 6 secs completing the TCP 3-way handshake.

This above issue occured while I was trying to access the facebook.com with FireFox 22.0.  After the TCP 3-way handshake was completed, Client waits for 6 seconds and sends the FIN for the last Seq Num that server sent.

Pcap taken in the client attached

https://www.dropbox.com/s/9yhvms85vdk2mku/facebook_windows-scale%20packet.pcapng

Few weeks back i had enabled the tcp tunning. NO hardware change, no new software installed.

Client-  Lenovo-T430, running windows 7 ent edition. Version 6.1 SP1.

NIC - Intel 82579LM Gig, driver - 11.15.16.0,

This continued for next 2 days laptop was rebooted several times. All of sudden, it started working again now.

Any idea on this?

Thanks,

Rewanta