Blocking websites on a Mac computer for Safari is relatively easy to set up using Mac OS X Mavericks Parental Controls. You can limit access to adult websites or any website you specify for any non-administrator account. Before handing a computer over to an employee or child, however, it's important that you test the settings first, since Parental Controls also blocks access to all secure websites, whether you intended to block them or not.
Step 1: Open Parental Controls
Launch System Preferences from the Apple menu and select Parental Controls. Click the Lock icon and enter your admin password when prompted. Select a user account, or add a new user account by clicking the + icon.
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Step 2: Block Websites
Click the Web tab and then select the Try to Limit Access to Adult Websites Automatically option. This blocks most websites featuring adult content unsafe for the workplace.
Step 3: Select Custom Sites
Click the Customize button to specify websites that you want to block or allow. To enter a website, click the + icon and enter the website's address.
Step 4: Block Other Browsers
Using another browser like Google Chrome or Mozilla Firefox bypasses Apple's Parental Controls. To prevent this, click the Apps tab and then expand the Other Apps icon in the Allowed Apps pane. Click the other Web browsers installed on the Mac to deselect them. Note that you can also limit access to adult content on the App Store here as well.
Click the Lock icon to prevent future changes to parental controls without an admin password.
Test Parental Controls
Step 1: Test Blocked Websites
Restart the Mac and log in with the restricted account. Launch Safari and then navigate to a website that you want blocked. A notification appears stating that the site can't be accessed.
Step 2: Add Websites as Prompted
Go to several websites that you want to keep accessible. If the website is blocked, click the Add Website button and then enter your admin username and password to add it to the Parental Controls white list.
Parental Controls restricts access to all secured websites -- those that begin with "https://" -- including websites that serve ads, share buttons or other content to the websites that you do want to access. Expect to see multiple pop-ups prompting you to add these websites to the Parental Controls white list. If you don't add them now, they will continue to pop up the next time anyone logs in with the restricted account.