Chrome only: Google Chrome extension Chrome Nanny prevents you from wasting time on distracting websites, so you can get things done instead of checking Facebook all day long.
Chrome Nanny is actually a port of the most important features of the Leech Block extension for Firefox, allowing you to create sets of URLs to block, by a particular time of day or a total number of minutes each day allowed for time-consuming websites. You can use regular expressions in the URL set, and even check statistics on what has been blocked. Chrome Nanny is a free download, works anywhere Chrome extensions do.
Chrome Nanny [Chrome Extensions]