You want to stop yourself from visiting certain sites? This browser extension can help you.
Don't Visit blocks access to specifiable sites or pages. By default it blocks the specified sites or pages completely, but if desired it can also provide the option to suspend a block for a couple of minutes.
Open the options page (you can find it by right-clicking the icon and selecting "Settings", by clicking "More Tools>Extensions" in the menu or by typing "chrome://extensions" in the address bar) to add or remove blocked sites.
Please note: This extension is intended to help with productivity or self-control, it's not supposed to wall sites from third parties, since the extension can always be disabled or uninstalled if desired.