The simplest way to block a website in Firefox

Firefox does not have a built-in website blocker in its main settings, but you can block sites in two practical ways: by using Firefox's parental controls (which work on any account), or by installing a free extension that does the blocking for you. The parental controls method requires no extra software and works when ready. The extension method gives you more control over which sites to block and when.

If you want to block a site right now without installing anything, the fastest route is Firefox's Restricted Browsing mode, which is designed for parents but works for anyone. If you want ongoing blocking that remembers your list, you will need a browser extension — the most straightforward options are LeechBlock NG or Freedom, both free and widely used.

Key Takeaways

  • Firefox's Restricted Browsing mode blocks sites when ready without installing extensions, but you must enable it each time you open the browser.
  • LeechBlock NG is a free extension that remembers which sites you blocked and can schedule blocking by time of day or day of week.
  • To block a site using Restricted Browsing, open Firefox, select the menu, choose Preferences, then Parental Controls, then enable Restrict Access to Adult Content.
  • Extensions like LeechBlock NG let you block sites on a schedule — for example, blocking social media during work hours but allowing it in the evening.
  • Blocked sites will show an error page when you try to visit them, but you can unblock them at any time through the same settings where you blocked them.

Using Firefox's built-in Restricted Browsing mode

Firefox includes a parental controls feature called Restricted Browsing that blocks adult content and can be used to restrict access to specific websites. This method requires no extensions and works when ready, but the restriction only stays active while you are using that browsing mode.

To turn on Restricted Browsing, open Firefox and click the menu button (three horizontal lines) in the top right corner. Select Preferences, then click Parental Controls on the left side. Check the box next to Enable Parental Controls. Firefox will then block sites it categorizes as adult content. When you close and reopen Firefox, you will need to enable this mode again — it does not stay on by default.

This method works well if you want a quick block that does not require setup, but it only blocks sites Firefox has already categorized. If you want to block a specific website that is not in Firefox's adult content list, or if you want the block to stay active every time you open the browser, you will need to use an extension instead.

Installing LeechBlock NG to block specific websites

LeechBlock NG is a free extension that lets you create a list of sites to block and set schedules for when the block is active. Unlike Restricted Browsing, it remembers your blocked sites and can block any website you choose, not just those Firefox has categorized.

To install LeechBlock NG, open Firefox and go to the Firefox Add-ons page (you can search "LeechBlock NG" or visit addons.mozilla.org). Click Add to Firefox on the LeechBlock NG page. Firefox will ask you to confirm — click Add. The extension will install in seconds and a new icon will appear in your toolbar (usually in the top right corner).

Once installed, click the LeechBlock NG icon to open its menu. Click Options to set up your blocked sites. In the options page, you will see a field labeled Blocked sites — type the website address you want to block (for example, facebook.com or reddit.com). You can add multiple sites by putting each one on a new line. Click Save at the bottom. The sites are now blocked — if you try to visit them, you will see a message saying the site is blocked.

Setting up time-based blocking with LeechBlock NG

LeechBlock NG can block sites only during certain hours or on certain days, which is useful if you want to allow access at some times but not others. For example, you might block social media during work hours but allow it in the evening.

Open the LeechBlock NG options page again by clicking the extension icon and selecting Options. Below the Blocked sites field, you will see Time-based blocking. Check the box to enable it. You can then set specific times — for example, 9 AM to 5 PM on weekdays — when the sites will be blocked. LeechBlock NG will automatically enforce this schedule every day.

If you want to block sites all day, every day, you can leave the time settings empty or set them to cover the full 24 hours. The extension will remember your settings even after you close and reopen Firefox.

Using Freedom to block websites across all your devices

Freedom is another free extension that blocks websites, with the added feature that it can sync your blocked sites across multiple devices if you sign up for a free account. If you use Firefox on both a computer and a phone, Freedom can block the same sites on both devices at once.

To install Freedom, search for it on the Firefox Add-ons page and click Add to Firefox. After installation, click the Freedom icon in your toolbar and sign up for a free account using your email. Once you are logged in, you can add sites to your blocked list. Any sites you block will appear on all your devices where you have Freedom installed and logged in.

Freedom also offers scheduling similar to LeechBlock NG, so you can set specific times when blocking is active. The free version covers the basics — blocking sites and scheduling — while a paid version adds features like blocking apps on your phone, but the free version is sufficient for website blocking alone.

What happens when you try to visit a blocked site

When you try to visit a site you have blocked, Firefox will show an error page instead of the website. The page will say something like "This site is blocked" or display the extension's blocking message. You will not be able to see the website content — the block prevents the page from loading at all.

If you change your mind and want to unblock a site, you can do so through the same extension menu where you added it. Open the extension options, find the site in your blocked list, delete it, and save your changes. The site will be accessible again the next time you try to visit it. If you set up time-based blocking, the site will become accessible once the blocked time window ends.

Removing or disabling a website blocker

If you want to stop using a blocker entirely, you can disable or remove the extension. To disable it temporarily without removing it, click the Firefox menu, go to Add-ons and Extensions, find the extension in the list, and click the toggle to turn it off. The extension will remain installed but will not block anything until you turn it back on.

To remove the extension completely, open Add-ons and Extensions, find the extension, and click the three dots next to it, then select Remove. Firefox will uninstall the extension when ready, and all your blocked sites will no longer be blocked. If you reinstall the extension later, you will need to set up your blocked sites list again — the old list will not be saved.

Frequently Asked Questions

Can someone else unblock a website I blocked?

If you are the only person using your Firefox account, no — they would need access to your Firefox settings to change the blocked sites list. If you share a computer with others who have their own Firefox accounts, each account has its own extensions and settings, so blocking in one account does not affect another. If you want to prevent someone from unblocking sites, you would need to set a password on your Firefox account or use parental control software at the operating system level.

Will blocking a website in Firefox block it in other browsers?

No. Firefox extensions only work in Firefox. If you want to block sites in Chrome, Edge, or Safari, you would need to install a separate blocker in each browser. Some extensions like Freedom work across multiple browsers if you install them in each one and log into the same account, but the blocking is not automatic — you have to set it up in each browser separately.

Can I block a website on my phone using Firefox?

Firefox on mobile phones does not support extensions the way desktop Firefox does, so LeechBlock NG and similar blockers will not work on your phone. However, Freedom offers a mobile app that can block sites on your phone if you sign up for their service. Alternatively, you can use your phone's built-in parental controls or screen time settings to restrict access to websites.

What if a website changes its address or uses a different domain?

If a site you blocked moves to a new address, you will need to add the new address to your blocked list. For example, if you blocked example.com and it moves to example.net, you would need to block example.net separately. Some extensions let you block by keyword — for example, blocking anything with "example" in the address — but most work by exact domain match.

Does blocking a website slow down Firefox?

No. Website blockers like LeechBlock NG and Freedom have minimal impact on Firefox's speed. They check each site you visit against your blocked list, which happens almost when ready. You will not notice any slowdown in browsing.