Firefox doesn't have a built-in site blocker, but you can use free add-ons to prevent access to specific websites

Firefox itself doesn't come with a native feature to block sites. Instead, you install a browser extension — a small program that adds functionality to Firefox. The most straightforward options are LeechBlock NG and Freedom, both free, both available directly from Firefox's add-on store. LeechBlock NG is lighter and simpler; Freedom is more powerful but requires more setup. Either one will prevent you from visiting a blocked site, even if you type the address directly into the address bar.

Why block a site at all? Common reasons include stopping yourself from visiting time-wasting platforms during work hours, keeping distracting social media out of reach, or preventing accidental visits to sites you're trying to avoid. A blocker creates friction — you have to actively remove the block to get through, which gives you a moment to reconsider.

Key Takeaways

  • LeechBlock NG and Freedom are the most popular free Firefox add-ons for blocking websites, and both prevent access even if you type the URL directly.
  • LeechBlock NG is simpler to set up and works best if you want to block specific sites or set time-based restrictions.
  • Freedom is more powerful and can block sites across all your browsers and devices, but requires an account and more configuration.
  • Once a site is blocked, you can still unblock it if you change your mind, though some add-ons let you set a delay before unblocking takes effect.

How to block a site using LeechBlock NG

LeechBlock NG is the simpler choice for most people. Start by going to the Firefox add-ons page — click the menu button (three horizontal lines) in the top right of Firefox, then select "Add-ons and themes." Search for "LeechBlock NG" and click "Add to Firefox." Firefox will ask you to confirm; click "Add."

Once installed, click the LeechBlock icon in your toolbar (it looks like a red circle with a line through it). Click the gear icon to open settings. Under "Sites," paste or type the full web address of the site you want to block — for example, reddit.com or twitter.com. You can add multiple sites, one per line. Click "Save" and you're done. The next time you try to visit that site, you'll see a blocked page instead.

If you want to block a site only during certain hours — say, 9 a.m. to 5 p.m. on weekdays — go back to settings and click "Times." Set your blocked hours, then assign those hours to the sites you listed. LeechBlock will only enforce the block during those windows.

How to block a site using Freedom

Freedom is more powerful but requires more steps. Go to the Firefox add-ons page, search for "Freedom," and click "Add to Firefox." You'll be asked to create a free account with Freedom — use an email address and password. After you log in, the Freedom dashboard opens in a new tab.

Click "Create a Session" or "Add a Blocker." Choose "Block Websites," then type the site you want to block. You can set when the block starts and how long it lasts — for example, "block every weekday from 8 a.m. to 6 p.m." or "block for the next 2 hours." Once you save, the block is active across all your devices if you're logged into the same Freedom account.

Freedom also blocks sites on your phone and computer if you install the app, which LeechBlock does not. The trade-off is that Freedom requires an account and syncs your blocks to their servers, whereas LeechBlock stores everything locally on your computer.

What happens when you try to visit a blocked site

When you navigate to a blocked site, Firefox stops the page from loading and shows you a message instead. With LeechBlock, you see a simple "This site is blocked" page with an option to unblock it. With Freedom, you see a similar message, but Freedom may show you how much time is left in your block window.

If you click "Unblock," both add-ons will ask you to confirm — some versions require you to wait a few seconds before the button becomes active, which gives you time to change your mind. You can unblock a site immediately, but the point of the blocker is that the extra step makes you pause.

Unblocking a site or removing the add-on entirely

To unblock a single site in LeechBlock, open the add-on settings again, find the site in your list, and delete it. To unblock in Freedom, open the Freedom dashboard and turn off or delete the blocker rule.

If you want to remove the add-on altogether, go to Firefox's add-ons page, find the add-on you installed, and click the three-dot menu next to it. Select "Remove." The add-on uninstalls immediately, and any blocks it was enforcing stop working.

Choosing between LeechBlock NG and Freedom

Use LeechBlock NG if you want a lightweight tool that blocks specific sites on Firefox only, works offline, and doesn't require an account. It's best for blocking a handful of sites during work hours or study sessions.

Use Freedom if you want to block sites across multiple devices (phone, tablet, computer), need more detailed scheduling options, or want a tool that syncs your blocks everywhere you log in. Freedom costs money if you want advanced features, but the basic blocking is free.

Neither add-on is unbreakable — someone determined to access a blocked site can uninstall the add-on or use a different browser. These tools work best as a friction layer, not as a security measure. If you need to prevent someone else from accessing certain sites on a shared computer, that's a different problem that requires parental controls or device-level restrictions, not a browser add-on.

Frequently Asked Questions

Can I block a site on just one tab or window?

No. Both LeechBlock and Freedom block a site across all of Firefox. If you block reddit.com, you can't visit it in any tab or window. Some add-ons let you pause the block temporarily, but you can't block a site in one tab and allow it in another.

What if I block a site by accident?

Open the add-on settings and remove the site from your block list. In LeechBlock, click the add-on icon, then the gear, find the site, and delete it. In Freedom, open the dashboard and turn off the rule. The block lifts immediately.

Will blocking a site slow down Firefox?

No. LeechBlock NG is very lightweight and has almost no impact on Firefox's speed. Freedom uses slightly more resources because it syncs with their servers, but the difference is not noticeable on most computers.

Can I block a site on my phone too?

LeechBlock NG only works on Firefox for desktop. Freedom has apps for iPhone and Android, so if you use Freedom on your computer, you can set the same blocks on your phone. You'll need to install the Freedom app separately.

What if I forget my Freedom password?

Go to the Freedom login page and click "Forgot password." Enter your email address and Freedom will send you a reset link. You can then create a new password and log back in.