There are several reasons for which you might to want to block or unblock certain websites from access in your browser. Some employers do this to make sure that employees do not surf the Web while working. Parents also use parental controls in some browsers to prevent their children from viewing websites with certain content. Although some browsers do not have the built-in feature for blocking websites, they can perform this function through free add-ons. Internet Explorer and Safari, for example, come standard with the website-filtering feature, while Mozilla Firefox needs an add-on.
Internet Explorer comes with a built-in utility that allows blocking and unblocking of any website with just a few clicks. Go to Click on Tools --> Options, select Content Tab and then click "Enable" in the Content Advisor section. Click on the Approved Sites tab and then type in the name of the website you want to block (for example, *.nameofthewebsite.com). Click "Never" to restrict this website, then "Apply" and "OK." You will then be prompted to create a password to protect your setting from changes by another user.
To unblock a previously blocked website, click on the restricted web address in the Approved Sites tab and then click "Allow," "Apply" and then "OK."
Mozilla Firefox does not come standard with a content advisor utility, like Internet Explorer. However, you can download a browser add-on tool that will allow you to manage accessible websites. BlockSite (see References) allows you to both block and unblock the websites you do not want to visit and also create a password to protect these settings. Just use the Tools --> Add-ons and type the name of the websites to block. If you want to block all of the websites associated with a certain company type in "http://_.nameofthewebsite._" or "http://nameofthewebsite..*"
All you need to do to unblock a website from the restriction is to select the already blocked address and allow access within the same add-on.
Safari is also a Web browser that comes standard with the Mac OS X operating system. OS X itself has a built-in parental control utility that allows you to block and unblock websites for Safari. You need to create accounts for each of the users for your computer and then block websites individually for each account. After you set up the accounts, go to System Preferences of the operating system and select the account you want to set up the control for. Select Safari for configuration and type in the Web address you want to block. You will have to repeat the last step for each individual website.
To unblock you need to delete the websites configured to be blocked for access from the same utility.