This extension stops Facebook loading, then asks if you *really* wanna do that...
A simple chrome extension that temporarily blocks Facebook before asking if you really want to waste your time there. Clicking "OK" will let Facebook load normally, while clicking "Cancel" will (optionally) close the current tab. The prompt can be customised; enter that one reason why you shouldn't be browsing Facebook and the extension will remind you of it.
Get more done. Be less angry.