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