Firefox doesn't have a built-in website blocker, but you can use free add-ons to prevent yourself from reaching specific sites

Firefox's standard settings don't include a feature to block websites directly. However, you can install a free browser extension that does this job — the most straightforward option is LeechBlock NG, which lets you create a list of sites you want to avoid and blocks them during times you set, or blocks them permanently.

The process takes about five minutes: you install the extension from Firefox's add-on store, tell it which websites to block, and it starts working immediately. If you close Firefox and reopen it, the blocks stay in place. You can also set time-based blocking — for example, block social media sites during work hours but allow them in the evening.

This guide walks you through installing a blocker, setting up your blocked list, and adjusting the settings to match how you actually work.

Key Takeaways

  • Firefox requires an add-on to block websites because the browser itself has no built-in blocking feature.
  • LeechBlock NG is a free, widely-used extension that blocks sites you choose and can run on a schedule or all the time.
  • You install the extension in about two minutes, then add website addresses to a blocked list in the extension's settings.
  • Blocked sites show an error page when you try to visit them, and the block persists until you remove the site from your list.
  • You can set different blocking schedules for different times of day, or block sites around the clock.

Installing LeechBlock NG in Firefox

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

The first result should be LeechBlock NG with a blue icon. Click the blue "Add to Firefox" button. A popup will ask you to confirm — click "Add" again. Firefox will install the extension in a few seconds, and you'll see a notification that it's been added.

Once installed, you should see a small icon in the top right of Firefox (it looks like a stop sign). This is your quick access to LeechBlock's settings. You can click it anytime to open the extension's menu.

Adding websites to your blocked list

Click the LeechBlock icon in the top right of Firefox. A small menu will appear. Click "Options" to open the full settings page. You'll see several tabs at the top — click the one labeled "Block List".

In the "Block List" section, you'll see a text box with the label "Blocked sites". Click inside this box and type the website address you want to block. Type only the domain name — for example, type facebook.com, not "www.facebook.com" or "https://www.facebook.com". Press Enter after each site to add it to the list.

Add as many sites as you need, one per line. Common sites people block include facebook.com, twitter.com, reddit.com, youtube.com, and instagram.com. Once you've entered all your sites, the blocking starts immediately — you don't need to click a save button.

Testing that your blocks are working

Try visiting one of the sites you just blocked. Type the address into Firefox's address bar and press Enter. Instead of loading the site, you should see a page that says "LeechBlock NG" with a message that the site is blocked. This confirms the extension is working.

If you see the actual website instead of the block message, check that you typed the domain name correctly in your block list. Common mistakes include including "www." at the start or forgetting to remove spaces. Go back to LeechBlock's Options page, find the site in your list, and fix the spelling.

Setting up time-based blocking schedules

If you want to block sites only during certain hours — for example, 9 AM to 5 PM on weekdays — you can set a schedule instead of blocking sites all day. Click the LeechBlock icon and open Options again. Click the "Times" tab.

You'll see a weekly grid with hours across the top and days down the left side. Click on the hours and days when you want blocking to be active. The cells you click will turn blue, showing when LeechBlock will block your sites. For example, to block during work hours Monday through Friday, click the cells from 9 AM to 5 PM in the Monday through Friday rows.

Once you've set your schedule, close the Options page. LeechBlock will now only block your sites during the hours you selected. Outside those hours, you can visit the sites normally. This approach works well if you want to prevent distraction during work but don't want to block sites entirely.

Removing sites from your blocked list

If you want to unblock a website, click the LeechBlock icon and open Options. Go to the "Block List" tab and find the site you want to remove in the text box. Delete the entire line — select it and press Delete or Backspace — then close the Options page. The site is now unblocked.

You can also temporarily disable LeechBlock entirely by clicking the icon in the top right and selecting "Disable" from the menu. This turns off all blocking until you click the icon again and select "Enable". This is useful if you need to visit a blocked site urgently but don't want to remove it from your list permanently.

What to do if you can't access the block settings

If you click the LeechBlock icon and the menu doesn't appear, or if the Options page won't load, try restarting Firefox. Close the browser completely and open it again. This usually fixes temporary glitches with extensions.

If restarting doesn't work, uninstall and reinstall the extension. Go to about:addons, find LeechBlock NG in your list, click the three-dot menu next to it, and select "Remove". Then follow the installation steps above to add it back. Your blocked list will be gone, so you'll need to re-enter your sites, but this solves most problems.

Frequently Asked Questions

Can I block a website on just one device, or does it block everywhere I use Firefox?

Blocking only works on the device where you installed LeechBlock. If you use Firefox on your phone and your computer, you'll need to install the extension and set up your block list on each device separately. The blocks don't sync across devices.

What if I try to visit a blocked site and I really need to access it right now?

Click the LeechBlock icon and select "Disable" from the menu. This turns off all blocking temporarily. You can then visit the site. When you're done, click the icon again and select "Enable" to turn blocking back on. The site stays on your block list — you're just pausing the blocker, not removing the site.

Can someone else remove my blocked sites if they use my computer?

Yes, if someone has access to your Firefox browser, they can open LeechBlock's Options and delete sites from your block list. If you want to prevent this, you can set a password in LeechBlock's settings under the "Password" tab. Once you set a password, anyone trying to change your block list will need to enter it first.

Does blocking a website slow down Firefox?

No, LeechBlock uses very little computer power. You won't notice any slowdown in Firefox's speed or performance. The extension only checks website addresses as you type them — it doesn't run background processes that drain your battery or memory.

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

LeechBlock blocks entire domains, not individual pages. If you want to block only facebook.com/games but not the rest of Facebook, LeechBlock can't do that — it will block all of facebook.com. For more precise blocking, you would need a different extension, but most people find blocking the entire domain works better anyway.