The fastest way to block a website in Firefox

Firefox does not have a built-in website blocker in its main settings. To block a website, you need to install an extension — a small program that adds blocking features to your browser. The most straightforward option is uBlock Origin, which blocks ads by default but can also prevent you from visiting specific sites you choose.

Once installed, uBlock Origin lets you add any website to a blocklist. When you try to visit a blocked site, Firefox shows a blank page instead. The process takes about two minutes: install the extension, visit the site you want to block, click the uBlock Origin icon, and select the option to block that domain.

If you want something simpler that focuses only on blocking without ad-blocking features, LeechBlock NG is designed specifically for this purpose. It lets you set time-based blocks (block a site only during work hours, for example) and requires a password to unblock sites, which makes it harder to bypass when you change your mind.

Key Takeaways

  • Firefox requires an extension to block websites because the browser itself does not include a built-in blocker.
  • uBlock Origin is free, widely used, and can block specific websites while also filtering ads.
  • LeechBlock NG is a simpler alternative that focuses only on blocking and allows you to set schedules and password protection.
  • After installing an extension, you can block a site in seconds by visiting it and using the extension's menu.

Installing uBlock Origin and blocking your first site

Go to the Firefox Add-ons page by typing about:addons into your address bar and pressing Enter. In the search box at the top, type "uBlock Origin" and click the result by the author Raymond Hill. Click the blue "Add to Firefox" button, then confirm by clicking "Add" in the popup that appears.

Once installed, you will see the uBlock Origin icon (a red square with a play button) in your toolbar. Now visit any website you want to block. Click the uBlock Origin icon, then look for the power button icon at the top of the menu that appears. Click it, and the entire domain will be added to your blocklist. The next time you try to visit that site, Firefox will show a blocked page instead.

To see your full blocklist or remove a site from it, click the uBlock Origin icon and select the gear icon to open settings. Go to the "My filters" tab to see every domain you have blocked and delete any you no longer want to block.

Using LeechBlock NG for time-based and password-protected blocking

LeechBlock NG works differently from uBlock Origin. Instead of blocking ads, it focuses entirely on preventing access to sites you choose, and it lets you set rules like "block this site only between 9 a.m. and 5 p.m." or "block this site every day except weekends."

Install it the same way: go to about:addons, search for "LeechBlock NG" by James Anderson, and click "Add to Firefox." Once installed, click the LeechBlock icon (a chain link) in your toolbar. Click "Options" to open the settings page. In the "Sites" section, type the website address you want to block in the text field and click "Add site."

To set a time-based block, go to the "Times" section and choose which days and hours the block should be active. If you want to prevent yourself from disabling the block on impulse, go to the "Password" section and set a password — you will need it to change any settings or temporarily unblock a site.

Blocking websites for specific times of day

Both extensions allow time-based blocking, but LeechBlock NG makes it the main feature. You might block social media sites during work hours but allow them in the evening, or block gaming sites on weekdays only.

In LeechBlock NG, after adding a site to your blocklist, click the "Times" tab. You will see a weekly grid. Click the cells for the hours and days when you want the site blocked. For example, click Monday through Friday from 9 a.m. to 5 p.m., and the site will be inaccessible only during those times. Outside those hours, you can visit it normally.

uBlock Origin does not have built-in scheduling, but you can achieve something similar by disabling and re-enabling the extension at certain times. For most people who want time-based blocking, LeechBlock NG is the better choice.

What happens when you try to visit a blocked site

When you navigate to a blocked website in Firefox, you will see a simple page that says the site is blocked. With uBlock Origin, the page is mostly blank with a message at the top. With LeechBlock NG, you see a more detailed message explaining why the site is blocked and when it will be unblocked again.

If you have set a password in LeechBlock NG, you can click a button to temporarily unblock the site, but you will need to enter your password first. This friction — the extra step of typing a password — is intentional. It gives you time to reconsider before accessing a site you blocked on purpose.

Removing blocks or switching extensions

If you block a site and later want to unblock it, the process is quick. In uBlock Origin, click the icon, then click the power button again next to the domain name. In LeechBlock NG, click the icon, go to "Options," find the site in the "Sites" list, and click the delete button next to it.

If you install both extensions, they will not conflict with each other, but you will have two icons in your toolbar. Most people choose one or the other. If you decide uBlock Origin is not right for you, go to about:addons, find it in your list, and click "Remove." The same applies to LeechBlock NG.

Uninstalling an extension removes all its blocks immediately. Any sites you blocked will become accessible again the moment you remove the extension.

Other blocking options: parental controls and DNS-level blocking

Firefox extensions work only in Firefox. If you want to block a website across your entire computer — in Chrome, Safari, or any other browser — you need a different approach. DNS-level blocking works at your internet connection level and blocks a site in every browser and app on your device.

To set up DNS blocking, you change your computer's DNS settings to use a service like Cloudflare's 1.1.1.1 for Families or OpenDNS. These services let you add domains to a blocklist, and they prevent your device from connecting to those sites no matter which browser you use. The setup is more technical than installing an extension, but it is more powerful.

If you are setting up blocks for a child, your operating system also has built-in parental controls. Windows has Family Safety, and macOS has Screen Time. These tools let you block websites and set time limits on app usage across the entire device. They are simpler than DNS blocking but less flexible.

Frequently Asked Questions

Can I block a website on my phone using Firefox?

Firefox on Android and iOS supports fewer extensions than the desktop version. uBlock Origin is available on Android but not iOS. For phone blocking, you will need to use your device's built-in parental controls or a separate app designed for mobile blocking.

Will blocking a website in Firefox also block it in Chrome or Safari?

No. Firefox extensions only work in Firefox. If you want to block a site across all browsers, use DNS-level blocking through a service like OpenDNS, or use your operating system's parental controls.

What if I forget my LeechBlock NG password?

If you set a password and forget it, you will need to uninstall and reinstall the extension. This removes all your settings and blocks. Write down your password somewhere safe, or use a password manager to store it.

Can websites detect that I have blocked them?

No. When you block a website, Firefox simply does not load the page. The website's server never receives a request from you, so it cannot tell whether you blocked it or simply chose not to visit.

Is uBlock Origin safe to use?

Yes. uBlock Origin is open-source, meaning its code is publicly available for anyone to review. It is maintained by Raymond Hill and is one of the most widely used browser extensions. It does not sell your data or display ads.