The simplest way to block a site in Firefox

Firefox does not have a built-in site blocker in its settings. Instead, you use an extension — a small program that adds features to your browser. The most straightforward option is LeechBlock NG, which is free and works on Windows, Mac, and Linux.

LeechBlock NG lets you create a list of websites you want to block, set the times when they are blocked, and choose whether to block them completely or just during certain hours. When you try to visit a blocked site, you see a message instead of the page.

Another popular choice is Freedom, which blocks sites across your entire computer (not just Firefox) and costs money. For most people, LeechBlock NG is enough.

Key Takeaways

  • Firefox does not block sites on its own — you need to install a free extension like LeechBlock NG from the Firefox Add-ons store.
  • After you install the extension, you add website addresses to a blocklist and set whether they are blocked all the time or only during certain hours.
  • When you try to visit a blocked site, the extension shows a message instead of loading the page.
  • If you want to unblock a site temporarily, most extensions let you pause blocking for a set amount of time without removing the site from your list.

How to install LeechBlock NG step by step

Open Firefox and go to the Firefox Add-ons page by typing about:addons in the address bar and pressing Enter. In the search box at the top, type "LeechBlock NG" and press Enter.

Click the blue "Add to Firefox" button next to LeechBlock NG. A popup will ask you to confirm — click "Add" again. Firefox will read and install the extension in a few seconds. You will see a small icon appear in the top right corner of your browser window.

Click that icon to open LeechBlock NG's settings. This is where you add the sites you want to block.

Adding websites to your blocklist

In LeechBlock NG's settings, you will see a section labeled "Block these sites" or "Blocked sites." Click in the text box and type the website address you want to block — for example, reddit.com or youtube.com. You do not need to type "https://" or "www." — just the domain name works.

If you want to block multiple sites, type each one on a new line. LeechBlock NG will block that site and all of its pages (like reddit.com/r/gaming or youtube.com/watch).

After you add your sites, scroll down and look for "Time allowance" or "Block times." This is where you decide whether the sites are blocked all day or only during certain hours. If you want them blocked all the time, set the time allowance to zero minutes.

Setting block times so sites are only blocked during certain hours

If you want to block a site only during work hours or study time, LeechBlock NG lets you set a schedule. In the settings, find the section for "Start time" and "End time" or "Active times."

Type the hour you want blocking to start — for example, 9:00 for 9 a.m. — and the hour you want it to end, like 17:00 for 5 p.m. The extension uses 24-hour time, so 13:00 is 1 p.m. and 22:00 is 10 p.m.

You can also choose which days of the week the block is active. If you only want to block sites Monday through Friday, uncheck Saturday and Sunday. Outside those times and days, you will be able to visit the sites normally.

What happens when you try to visit a blocked site

When you click a link to a blocked site or type its address in the address bar, Firefox will not load the page. Instead, you will see a message from LeechBlock NG saying the site is blocked, along with the reason (if you added one) and how long until it is unblocked.

Most extensions also show a countdown timer so you know when the block ends. This is intentional — it is meant to discourage you from trying to find a workaround.

Pausing or temporarily unblocking a site

If you need to visit a blocked site for a legitimate reason — like checking work email during a break — most extensions let you pause blocking for a set time without removing the site from your list.

In LeechBlock NG, click the extension icon and look for a "Pause" or "Disable" button. You can usually pause for 5, 15, 30, or 60 minutes. After that time passes, blocking turns back on automatically. This prevents you from pausing indefinitely and defeating the purpose of the blocker.

Other extensions that block websites

Cold Turkey is a more aggressive blocker that prevents you from uninstalling it or restarting your computer to get around the block. It costs money but is popular with people who need a stronger barrier.

StayFocusd is lighter and focuses on limiting time spent on sites rather than blocking them completely — you can set a daily time budget, and once you hit it, the site is blocked for the rest of the day.

Freedom blocks sites across your entire computer, not just Firefox, and syncs across your phone and tablet. It also costs money but works if you need to block sites in other browsers or apps.

For most people, LeechBlock NG is free, straightforward, and does the job. Start there before paying for something more complex.

Frequently Asked Questions

Can I block a site on just one device, or does it block everywhere?

LeechBlock NG only blocks sites in Firefox on the device where you installed it. If you use Firefox on your phone, you would need to install the extension there separately and set up the same blocklist. Other browsers like Chrome or Safari are not affected.

What if I forget the password to unblock a site?

LeechBlock NG does not have a password feature built in. If you want to add a password so you cannot unblock sites on impulse, you can set one in the extension's settings under "Password protection." Write the password down somewhere safe — if you lose it, you may need to uninstall and reinstall the extension.

Can I block a specific page instead of the whole website?

LeechBlock NG blocks the entire domain, so if you block reddit.com, you cannot visit any page on Reddit. Most extensions work this way because blocking individual pages is straightforward to get around. If you need finer control, Freedom offers more detailed blocking options.

Does blocking a site slow down Firefox?

No. LeechBlock NG runs in the background and only checks URLs when you try to visit them. It uses very little memory and will not make Firefox noticeably slower.

Can someone else remove my blocklist if they use my computer?

Yes, unless you set a password. Anyone with access to your Firefox settings can uninstall the extension or change the blocklist. If you share a computer and want to prevent this, enable password protection in LeechBlock NG's settings.