I recommend this extension for Chrome. It limits the time you spend on websites that make you waste your time.
StayFocusd increases your productivity by limiting the amount of time that you can spend on time-wasting websites.
[As seen in The New York Times, The Wall Street Journal, The Washington Post and U.S. News And World Reports, and on Lifehacker, Mashable, PCMag, CNET, ReadWriteWeb, Gizmodo, GigaOm, MaximumPC, The Huffington Post, MakeUseOf, MSNBC, and more!]You sit down at the computer, and you swear you'll be productive. Next thing you know, it's twelve hours later. You've checked your email, updated your Facebook status, browsed the trending topics on Twitter, read your RSS feeds, looked up your favorite band on Wikipedia, vanity googled yourself, cyber-stalked your ex, looked at all your high-school crushes' Facebook photos, watered your plants on Farmville, and lost a week's pay playing online poker. What you haven't done is WORK.StayFocusd is a productivity extension for Google Chrome that helps you stay focused on work by restricting the amount of time you can spend on time-wasting websites. Once your allotted time has been used up, the sites you have blocked will be inaccessible for the rest of the day.It is highly configurable, allowing you to block or allow entire sites, specific subdomains, specific paths, specific pages, even specific in-page content (videos, games, images, forms, etc).
You can set the amount of time you will dedicate to websites like yahoo, youtube, reddit (and links found there), etc. Once the time is over you will be unable to access those websites... until the next day OR you can block certain websites for a certain amount of time (nuclear option). It can run in incognito mode and it's only available for Chrome so I recommend to uninstall Firefox, Safari and any other browser you have on your laptop.
Read the FAQ's, customize options are explained there.
It's a good tool for setting a new habbits to surf the web but you have also to be committed otherwise you will find always a way to cheat.
"Take what you need and leave the rest." I got nothing but moments to live.