just as it says, it doesn't happen anymore if I uninstall the firewall part of AIS, and happens again when I reinstall it. I got to wait 15/30 secs to get a connection when the system wakes up from sleep mode. Actually what's funny is that the connection itself seems OK for Windows (anything related to the network gives green light), but down for Firefox and Thunderbird
Sometimes the waiting isn't enough, I must disconnect and reconnect to my router for things to work again. I think the firewall is the culprit somehow, although I can't show how. Again, the connection is there but is temporary down for browsing and getting mails.