Usually, educational institutes and corporate houses block.These days, Internet filtering and controlled access is the new trend.great website unblocker that will unblock websites for you.

In the menu bar, select Tools > Options. Then select the Content tab. Select the "Exceptions" button in front of the the "Block pop-up windows" setting. A list of "Allowed sites" would be displayed. Select the site which you wish to block and select "Remove site". More information and screenshots in this article.