Firefox doesn't have a built-in website blocker, but you can use free add-ons to prevent yourself from visiting specific sites
Firefox itself has no native feature to block websites. Instead, you install a small program called an add-on (also called an extension) that sits in your browser and stops you from reaching the sites you choose. The most straightforward options are LeechBlock NG, Freedom, and Cold Turkey Blocker — all free or low-cost, all available directly from Firefox's add-on store.
The process takes about five minutes: you find the add-on, install it, tell it which websites to block, and set when the block applies. Once active, trying to visit a blocked site shows you a warning page instead of the actual website. Some blockers let you set a timer you can't override; others let you disable the block temporarily if you really need to. The choice depends on whether you're blocking for focus (where a timer helps) or for safety (where you want it harder to bypass).
Key Takeaways
- Firefox add-ons like LeechBlock NG and Freedom block websites by intercepting your request before it reaches the site and showing a stop page instead.
- You can set different blocking schedules — all day, only during work hours, or only on weekdays — depending on why you're blocking.
- Some blockers let you set a timer you cannot skip; others let you disable the block if you choose, so pick based on how much willpower you want the tool to enforce.
- Blocking works only in Firefox; if you use Chrome, Safari, or Edge on the same computer, those browsers will not respect the Firefox blocker.
How to install a website blocker in Firefox
Open Firefox and go to the Add-ons page by clicking the menu button (three horizontal lines) in the top right, then selecting "Add-ons and themes." In the search box at the top left, type "LeechBlock NG" — this is the most popular free option and works well for most people. Click the blue "Add to Firefox" button. A popup will ask you to confirm; click "Add" again.
Once installed, you'll see a small icon appear in your toolbar (usually in the top right area of Firefox). Click that icon to open the blocker's settings. This is where you enter the websites you want to block. Type the domain name — for example, "reddit.com" or "youtube.com" — and the blocker will stop you from visiting that site or any page within it. You can add as many sites as you need.
Setting up blocking schedules and timers
LeechBlock NG lets you choose when the block is active. Click the settings icon (usually a gear) inside the add-on to see options like "Block during these times" or "Block on these days." You can set it to block only Monday through Friday, only between 9 a.m. and 5 p.m., or all day every day. This is useful if you want to allow yourself access to a site outside work hours but prevent it during the times you're trying to focus.
Some blockers, like Freedom, also let you set a countdown timer. Once you set up the blocker, it runs for a set time — say, two hours — and you cannot turn it off early. This removes the temptation to disable the block the moment you feel bored. Other blockers like Cold Turkey Blocker offer a "frozen turkey" mode where the block is nearly impossible to bypass without restarting your computer, which is stronger but also more disruptive if you genuinely need access to something.
What happens when you try to visit a blocked website
When you click a link to a blocked site or type its address into the address bar, Firefox stops the page from loading and shows you a warning page instead. The page usually says something like "This site is blocked" and displays the name of the blocker that stopped you. Some blockers show a motivational message or let you customize what the warning page says.
If your blocker has a timer or bypass option, you'll see a button to disable the block temporarily — but it might require you to wait a certain amount of time first, or it might ask you to confirm your choice twice. This friction is intentional; it gives you a moment to reconsider before you override the block.
Choosing between different blockers based on your needs
LeechBlock NG is free and works well if you want basic blocking with flexible schedules. It's lightweight and doesn't slow down Firefox. Use this if you're blocking sites to stay focused during work or study and you want to allow yourself access outside those hours.
Freedom is free for basic use and adds a timer you cannot skip once activated. It blocks across all your browsers and devices if you pay for the full version, but the free Firefox version works fine if you only use Firefox. Use this if you need something stronger than willpower alone — the timer forces you to wait before you can unblock a site.
Cold Turkey Blocker is paid (around $39 one-time) but offers the strongest enforcement, including a "frozen turkey" mode that requires a computer restart to bypass. Use this only if you've tried other blockers and found them too straightforward to disable, or if you're blocking sites for safety reasons rather than focus.
Blocking websites across all your browsers
Firefox blockers only work in Firefox. If you use Chrome, Safari, or Edge on the same computer, those browsers will not see the Firefox blocker and you can visit blocked sites freely. If you need to block a site across all browsers, you have two options: install the same blocker in each browser (most popular blockers are available for Chrome and Edge), or use a system-level blocker that works at the router or operating system level.
For most people, installing the blocker in each browser you actually use is simpler. If you only use Firefox, you don't need to worry about this. If you switch between Firefox and Chrome, install the blocker in both.
Removing or temporarily disabling a blocker
If you decide you no longer want to block a site, click the blocker's icon in your toolbar and remove the site from the list. The block stops when ready. If you want to disable the entire blocker without uninstalling it, go back to Firefox's Add-ons page, find the blocker, and click the toggle to turn it off. You can turn it back on anytime.
If you need to uninstall the blocker completely, go to Add-ons, find it in your list, and click the three-dot menu next to it, then select "Remove." Firefox will ask you to confirm. After you confirm, the blocker is gone and all sites are accessible again.
Frequently Asked Questions
Can I block a website on just one device, or does it block everywhere I use Firefox?
Blocking works only on the device where you installed the add-on. If you use Firefox on your phone and your computer, you need to install the blocker on both if you want the same sites blocked on both. Firefox does not sync add-ons across devices automatically.
What if I forget the name of a website I want to block?
You can usually find the domain name by looking at the address bar when you're on the site. For example, if you're on Reddit, the address bar shows "reddit.com" — that's what you enter into the blocker. If you're on a specific page like a subreddit, just use "reddit.com" and the blocker will stop all Reddit pages.
Does blocking a website slow down Firefox?
No. Website blockers use very little computer power. You won't notice any slowdown in Firefox's speed or performance, even if you're blocking dozens of sites.
Can someone else disable my blocker if they use my computer?
Yes, if they have access to your Firefox account and know how to open Add-ons, they can disable or remove the blocker. If you need to prevent someone else from disabling it, you would need to set a Firefox password or use a system-level blocker instead, which is more complex.
What's the difference between blocking a website and deleting my browsing history?
Blocking prevents you from visiting a site going forward. Deleting history removes the record that you visited a site in the past. They do different things — blocking is about the future, history deletion is about the past.