Firefox doesn't have a built-in site blocker, but you can use free add-ons to stop yourself from reaching specific websites

Firefox's browser settings alone won't block sites — you need to install an extension that does the blocking for you. The most straightforward option is LeechBlock NG, a free add-on that lets you name websites you want to avoid and set times when they're blocked. Another popular choice is Cold Turkey Blocker, which is harder to disable once you've set it up. Both work the same way: you give them a list of sites, and when you try to visit one, you hit a block page instead of the website.

The reason Firefox requires an add-on is that blocking is a personal choice, not a security feature. Firefox treats all websites the same way by default. An add-on sits between you and the internet and intercepts requests to the sites you've listed, stopping them before they load.

Key Takeaways

  • LeechBlock NG is the most popular free Firefox blocker and lets you set specific times when sites are blocked.
  • You install a blocker as a Firefox add-on, then give it a list of websites you want to avoid.
  • Some blockers like Cold Turkey are harder to turn off once activated, which makes them useful if you want to force yourself to stick to your block list.
  • Blocking only works in Firefox — the same sites will still load in Chrome, Safari, or Edge unless you install a blocker there too.

Installing LeechBlock NG, the easiest option

Open Firefox and go to the add-ons page by typing about:addons in the address bar and pressing Enter. You'll see a search box at the top left. Type "LeechBlock NG" and press Enter. The first result should be the official LeechBlock NG add-on — click the blue "Add to Firefox" button.

Firefox will ask you to confirm. Click "Add" in the popup that appears. The add-on installs instantly. You'll see a small icon appear in the top right of Firefox (it looks like a red circle with a line through it). That's your blocker.

Now click that icon to open LeechBlock's settings. You'll see a list of "Block Sets" — these are groups of sites you can block on different schedules. Click on "Block Set 1" to start adding websites. In the "Sites" field, type the addresses of the sites you want to block, one per line. For example, type reddit.com or twitter.com. You don't need to type "https://" — just the domain name works.

Below the sites list, you can set times when the block is active. If you leave the time fields blank, the sites stay blocked all day. If you want them blocked only during work hours, set a start time (like 9:00 AM) and an end time (like 5:00 PM). Click "Save" when you're done. The next time you try to visit one of those sites, you'll see a block page instead.

Using Cold Turkey Blocker for stronger blocking

Cold Turkey Blocker is harder to turn off once you've activated it, which makes it useful if you know you'll be tempted to disable the blocker. Go to about:addons, search for "Cold Turkey Blocker," and click "Add to Firefox." The installation is the same as LeechBlock.

Click the Cold Turkey icon in the top right to open settings. You'll see options to create a "Freeze" — a block that runs on a schedule you set. Type the websites you want to block in the "Websites" field. Set the days and times you want the block active. When the scheduled time arrives, Cold Turkey locks the sites and won't let you disable it until the time window closes.

The main difference from LeechBlock is that Cold Turkey is designed to be unbreakable during its active window. You can't just turn it off and visit the site anyway. This makes it better if you're blocking sites because you're trying to break a habit and you need the blocker to actually force your hand.

What happens when you try to visit a blocked site

When you navigate to a blocked website, Firefox stops the page from loading and shows you a block page instead. The page usually displays a message saying the site is blocked, along with a countdown timer if you set one. Some blockers let you set a custom message on the block page — you can use this to remind yourself why you're blocking the site.

You won't see the website's content at all. The blocker intercepts the request before Firefox even connects to the site's server. This is different from just closing a tab — the site never loads in the background.

Blocking sites on specific days or times only

Both LeechBlock and Cold Turkey let you set schedules. In LeechBlock, click the icon, select your Block Set, and look for the time fields. You can set different schedules for different days of the week. For example, you might block social media Monday through Friday from 9 AM to 5 PM, but leave it unblocked on weekends.

If you want a site blocked only on certain days, enter those days in the "Days" field. Most blockers use numbers (1 for Monday, 2 for Tuesday, and so on) or let you click checkboxes for each day. Check your blocker's help section if you're unsure of the format.

Cold Turkey's schedule works similarly but is built around "Freezes" — named blocks that run on a repeating schedule. You create one Freeze for work hours, another for evenings, and so on. Each Freeze has its own list of sites and its own schedule.

Blocking sites across multiple devices

A blocker installed in Firefox only works in Firefox on that specific computer. If you use Firefox on your phone, you'll need to install the blocker there too. If you use Chrome or Safari, you'll need to install a blocker in those browsers as well.

Some blockers like Cold Turkey have desktop versions that work across your entire computer, not just in the browser. These are usually paid options. The free Firefox add-ons only block within Firefox itself.

If you want to block sites on your phone, search your phone's app store for "website blocker" — iOS and Android both have free options. They work the same way as Firefox add-ons but are built into the phone's system.

Removing or changing your block list

To remove a site from your block list, open the blocker's settings, find the site in the list, and delete it. Save your changes. The site will be unblocked the next time you try to visit it.

To turn off the blocker entirely, go to about:addons, find the blocker in your list, and click the toggle switch next to it. The add-on stays installed but stops working. You can turn it back on the same way.

If you want to uninstall the blocker completely, click the three dots next to the add-on name in about:addons and select "Remove." The add-on disappears from Firefox, and all your block lists are deleted.

Frequently Asked Questions

Can I block a site on just one device if I use Firefox on multiple computers?

Yes. Each Firefox installation has its own add-ons and settings. If you install LeechBlock on your work computer, it won't affect Firefox on your home computer. You'd need to install and configure the blocker separately on each device.

What if I forget the password to disable the blocker?

Most blockers let you set a password to prevent accidental disabling. If you forget it, you can uninstall the add-on from about:addons and reinstall it fresh. This deletes all your settings, so write down your block list before you uninstall.

Will the blocker work if I restart Firefox?

Yes. The blocker stays active across restarts unless you manually disable it. If you set a schedule, the blocker follows that schedule even if you close and reopen Firefox.

Can I block a site only on weekdays?

Yes. Both LeechBlock and Cold Turkey let you set different schedules for different days. In LeechBlock, select the days you want the block active (usually Monday through Friday). The site will be unblocked on weekends.

Does blocking a site in Firefox block it in other browsers too?

No. A Firefox blocker only works in Firefox. If you want to block sites in Chrome, Safari, or Edge, you need to install a separate blocker in each browser.