Block websites in Mozilla Firefox using Windows parental controls or Firefox third-party filtering extensions.
Filter Websites Using Windows Parental Controls
In Microsoft Windows 8.1 and 7, set up parental controls to block access to certain websites or categories of websites, or to allow access only to certain, whitelisted sites that you specify.
Mozilla Firefox and other browsers will follow parental controls for your computer's operating system.
Configure parental controls, including Web filtering, through the Control Panel.
Click the Start Menu.
Click the Control Panel icon.
Click Set Up Family Safety for Any User.
Click the user account for parental controls.
Click the On, Enforce Current Settings radio button under Family Safety.
Click Web Filtering.
Click the Can Only Use the Websites I Allow radio button, then click Set Web Filtering Level.
Choose a restriction level that's appropriate for your needs, allowing only specific sites you'll specify or allowing only particular types of sites. Then, click Allow or Block Websites to further customize which websites are permitted.
Enter the address of any specific website to allow or block, and click the Allow or Block buttons. Continue until you've addressed all the specific websites to allow or block.
Use Third-Party Filtering Extensions
You can also filter websites in Firefox using third-party filtering extensions available from the Firefox Add-Ons page.
MetaCert's Parental Controls & Web Filter extension syncs its list of blocked, adult-oriented sites with a list from its own websites, so it can filter newly posted content quickly. It's also available for other browsers.
FoxFilter allows you to filter websites by address, category or by particular keyword that appears on the site. An ad-supported version with basic features is free, and you can pay for a version with no ads and added features, like syncing across computers.
Whitelist Ninja allows access only to sites on a particular list, which you can customize with a password.