Only facebook and not just in Safari.
Try using OpenDNS for better speed, more security, includes anti phishing filters, and it's free.
Open System Preferences then select Network. Click the Advanced tab then click the DNS tab.
Enter these addresses exactly as you see them here.
Then click OK and restart your Mac, launch Safari, try Facebook.
If that didn't help, all you have to do is go back to the DNS tab and delete those addresses.
More about OpenDNS here > Topic : Manually provided DNS server addresses are higher priority than DHCP's
edited by: cs