Why can't I block Facebook using /etc/hosts on Mountain Lion (OS X)?

It worked for a while in the old configuration, but then stopped working for some reason.

Here is my /etc/hosts file from my Mountain Lion MacBook Air:

127.0.0.1 reddit.com www.reddit.com
127.0.0.1 facebook.com www.facebook.com
##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1       localhost
255.255.255.255 broadcasthost
::1             localhost
fe80::1%lo0     localhost

This blocks Reddit,but not Facebook.

I've tried flushing the DNS cache for the machine ("sudo killall -HUP mDNSResponder"), the bowsers (FF and Chrome) and I've tried restarting the computer.

And I've moved the entries to the top of the file on the advice of this article, but it didn't work before when it was at the bottom either. Each time it would block Reddit but not Facebook.

harrymc is close but for some reason OS X (as of 10.8.2) doesn't respect the IPv6 loopback address of ::1 (probably a bug), so you have to use fe80::1%lo0. The reason you need to block IPv6 is because Facebook will serve you their site over V6 if your ISP supports it. You can easily verify this by installing a browser plugin that displays an icon when a site is being served via IPv6. The reason this wasn't a problem for you before is because Facebook likely only recently started serving their site over IPv6.

So the correct answer is:

# Block Facebook IPv4
127.0.0.1   www.facebook.com
127.0.0.1   facebook.com
127.0.0.1   login.facebook.com
127.0.0.1   www.login.facebook.com
127.0.0.1   fbcdn.net
127.0.0.1   www.fbcdn.net
127.0.0.1   fbcdn.com
127.0.0.1   www.fbcdn.com
127.0.0.1   static.ak.fbcdn.net
127.0.0.1   static.ak.connect.facebook.com
127.0.0.1   connect.facebook.net
127.0.0.1   www.connect.facebook.net
127.0.0.1   apps.facebook.com

# Block Facebook IPv6
fe80::1%lo0 facebook.com
fe80::1%lo0 login.facebook.com
fe80::1%lo0 www.login.facebook.com
fe80::1%lo0 fbcdn.net
fe80::1%lo0 www.fbcdn.net
fe80::1%lo0 fbcdn.com
fe80::1%lo0 www.fbcdn.com
fe80::1%lo0 static.ak.fbcdn.net
fe80::1%lo0 static.ak.connect.facebook.com
fe80::1%lo0 connect.facebook.net
fe80::1%lo0 www.connect.facebook.net
fe80::1%lo0 apps.facebook.com

Try adding following line in /etc/resolv.conf

lookup file, bind

This should force OS X to use /etc/hosts before dns. The only problem is if you use dhcp, this file will be overwrote each reboot.