I'm having the same problem. It was ok last thursday (7.2.2013).
When clicking this: http://www.facebook.com the page goes blank.
The same page opens normally on Firefox and Chrome.
I have the Os 10.6.8 and Safari 5.1.7
Try flushing the DNS cache. To do so,
1. Quit Safari.
2. Open Terminal.app (type 'Term' in the Spotlight searchbar) and paste the appropriate command for you version of OS X from below. Then press 'return' on your keyboard.
In Tiger (10.4)
In Leopard (10.5) / Snow Leopard (10.6)
In Lion (10.7) / Mountain Lion (10.8)
sudo killall -HUP mDNSResponder
With Lion/Mountain Lion, you’ll have to follow the command with your Admin password, which will be invisible when you type it.
3. Restart Safari and test.
Can you connect to another webpage with https,
e.g. gmail.com, twitter.com etc?
If not, then you need to repair your disk permissions (through Disk Utility).
If that doesn't work you 'll need to repair ACLs.