The simplest way to block a site in Firefox
Firefox does not have a built-in site blocker, but you can use a free extension called uBlock Origin to prevent yourself from visiting specific websites. Once installed, uBlock Origin lets you add any site to a blocklist — when you try to visit it, you see a message instead of the page.
The extension works on Windows, Mac, and Linux. It takes about two minutes to install and another minute to add your first blocked site. The block happens on your computer, so it only works in Firefox — if you use Chrome or Safari, you would need to set up blocking there separately.
If you want to block sites across all your browsers at once, or if you want to prevent yourself from unblocking sites without a password, you would need a different tool. But for a quick, free way to block one or two sites in Firefox alone, uBlock Origin is the standard choice.
Key Takeaways
- Firefox has no built-in site blocker, but the free extension uBlock Origin can block any website you choose.
- After you install uBlock Origin, you right-click a site and select "Block this site" to add it to your blocklist.
- A blocked site shows an error message instead of loading, but you can unblock it anytime by visiting the extension settings.
- Blocking only works in Firefox — other browsers need their own blockers unless you use a network-level tool like a router setting.
- If you want to prevent yourself from unblocking sites, you need parental control software or a different tool, not just an extension.
Installing uBlock Origin in Firefox
Go to the Firefox Add-ons page by typing about:addons in the address bar and pressing Enter. You will see a search box at the top left. Type "uBlock Origin" and press Enter.
The first result should be uBlock Origin with a red and white icon. Click the blue "Add to Firefox" button. 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 red icon appear in the top right corner of Firefox, next to your address bar.
That icon means uBlock Origin is now running. You do not need to do anything else to set up it — it is ready to use when ready.
Blocking your first website
Visit the website you want to block. Once the page loads, right-click anywhere on the page and look for an option that says "Block this site" or similar. Click it. A small window will appear asking you to confirm — click the button to confirm the block.
Refresh the page or try to visit it again. Instead of loading, you should see a message saying the site is blocked. The block is now active. If you visit that site again in Firefox, you will always see the blocked message instead of the actual page.
You can block as many sites as you want by repeating this process. Each one will be added to your blocklist automatically.
Unblocking a site if you change your mind
Click the uBlock Origin icon in the top right corner of Firefox (the red and white square). A menu will open. Look for a settings or options button — this is usually a gear icon or three horizontal lines. Click it to open the uBlock Origin settings page.
Find the section labeled "My filters" or "Blocklist". You should see a list of all the sites you have blocked. Find the one you want to unblock, and delete it from the list. Close the settings page and refresh Firefox. The site is now unblocked and will load normally again.
If you cannot find the blocklist in settings, try right-clicking on the blocked site's error message and look for an "Unblock" option. Different versions of uBlock Origin may arrange this slightly differently, but the option is always there somewhere.
Blocking sites across all your browsers at once
If you use Firefox, Chrome, Safari, and other browsers and want to block the same sites in all of them, an extension in each browser is not practical. Instead, you can change the settings in your router — the device that connects your home to the internet.
Most routers have a parental control or content filter section in their settings. You log into your router's admin page (usually by typing your router's IP address into a browser), find the filter section, and add websites to a blocklist. Any device on your home network will then be blocked from visiting those sites, regardless of which browser they use.
The exact steps depend on your router's brand and model. Your router's manual or the manufacturer's website will have instructions. This method is more powerful than an extension, but it also requires more setup and a basic understanding of your router's settings.
Preventing yourself from unblocking sites
uBlock Origin lets you unblock any site anytime by editing your blocklist. If you want to prevent yourself from unblocking sites — for example, to help you stay focused or to enforce a rule you have set for yourself — an extension alone will not work. You need software that requires a password to change settings.
Parental control software like Cold Turkey (Windows and Mac) or Freedom (Windows, Mac, iOS, and Android) can block sites and lock you out of changing the settings without a password. These are paid tools, but they offer much stronger blocking than a straightforward extension. Some also let you set schedules, so sites are only blocked during certain hours.
If you want free options, some router-level blockers also require a password to change settings. This prevents you from unblocking sites by straightforward changing your browser extension, because the block happens at the network level instead.
Why Firefox does not have a built-in blocker
Firefox is designed to be a general-purpose browser that works for everyone. A built-in site blocker would be a specialized tool that only some people need. Instead of building it into Firefox itself, the developers let extensions handle it. This keeps Firefox lightweight and lets you choose exactly which blocking tool you want.
Extensions also update independently of Firefox, so if a blocker needs to change how it works, it can do so without waiting for a Firefox update. This makes extensions more flexible than a built-in feature would be.
Frequently Asked Questions
Can I block a site without installing an extension?
No, Firefox has no native blocking feature. You must use an extension like uBlock Origin, or you must change your router settings to block sites across all devices. There is no way to block a site using only Firefox's built-in settings.
Will blocking a site in Firefox also block it on my phone?
No. Extensions only work in the browser where you install them. If you use Firefox on your phone, you would need to install uBlock Origin there separately and add the sites again. To block sites across all devices, use your router's parental controls instead.
What if I accidentally block a site I need?
Open uBlock Origin settings, find the site in your blocklist, and delete it. The site will unblock when ready. You can also right-click the blocked site's error message and look for an unblock option, depending on your version of uBlock Origin.
Does blocking a site hide it from my internet provider?
No. Blocking a site in Firefox only prevents your browser from displaying it — your internet provider can still see that you tried to visit it. If you want to hide your browsing from your provider, you need a VPN, which is a different tool entirely.
Can I block a site only during certain hours?
uBlock Origin cannot do this on its own. You would need parental control software like Cold Turkey or Freedom, which let you set schedules for when sites are blocked. These are paid tools but offer more control than a straightforward extension.