After I restarted my Firefox (MAC),12.0, Avast Webrep plugin NOT enabled), facebook no longer loaded.
As soon as turned off the webshield, facebook loads normal.
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:12.0) Gecko/20100101 Firefox/12.0
Mac OS X 10.6.8 (10K549), 8GB RAM
This seem to only happen on first connecton to fb. I turned webshield on and I can reload facebook.
The webshields activity graph shows no activity while this happens.
This is most probably caused by a misconfiguration of ipv6 on your machine. Try to disable ipv6 in the web/mail shield preferences (or at system level), it should fix this issue.
Should it not recover by itself from that, like try IPv4 if the IPv6 link is unavailable?
The problem with broken ipv6 when a proxy is used is, that the browser connection always succeeds as the browser is connecting to the (local) proxy, not the server. The connection is immediately closed by the proxy when it can not connect to the ipv6 address, but the browser does not retry the connection using ipv4 in this case.