The simplest way to block a website in Firefox
Firefox does not have a built-in website blocker in its main settings, but you can block sites in two practical ways: using parental controls if you are managing a device for someone else, or installing a free browser extension that does the blocking for you. The extension route is faster for most people and works when ready.
The most straightforward method is to install an extension called LeechBlock NG or Freedom, both free and widely used. These extensions let you type in the web addresses you want to block, set times when the block is active, and even add a password so you cannot easily turn them off on impulse. Once installed, they run in the background and stop you from reaching those sites.
If you are setting up Firefox for a child or someone else, Firefox's built-in Restricted Profiles feature lets you block entire categories of sites — adult content, gambling, violence — without needing an extension. This method requires a password to change, so the restrictions stay in place.
Key Takeaways
- Firefox does not have a native website blocker, but free extensions like LeechBlock NG add this feature in minutes.
- Extensions let you block specific websites, set times when blocks are active, and password-protect the settings so you cannot turn them off easily.
- Restricted Profiles, built into Firefox, block entire categories of content and work well if you are managing a device for someone else.
- Blocking a website in Firefox only affects that browser — the site remains reachable in Chrome, Safari, or other browsers on the same computer.
Installing a blocking extension in Firefox
Open Firefox and go to the address bar. Type about:addons and press Enter. This opens the Add-ons page where Firefox stores all extensions. In the search box at the top left, type LeechBlock NG and press Enter.
Click the blue Add to Firefox button next to LeechBlock NG. A popup will ask you to confirm — click Add. Firefox will install the extension in a few seconds. You will see a small icon appear in the top right corner of your browser, usually a red square or circle.
Click that icon to open the extension's settings. You will see a box where you can type website addresses you want to block. Type the full address — for example, reddit.com or twitter.com — and click Add. The site is now blocked. If you try to visit it, you will see a message saying the page is blocked instead of the actual website.
Setting times when blocks are active
Most blocking extensions let you choose when the block is on. This is useful if you want to block a site during work hours but allow it in the evening. Open the LeechBlock NG settings again by clicking its icon in the top right.
Look for a section called Times or Schedule. You can set specific hours — for example, 9 AM to 5 PM on weekdays — when the block is active. Outside those hours, you can visit the site normally. If you do not set a time, the block stays on all day.
Some extensions also let you set a password to change the settings. This prevents you from quickly turning off the block when you are tempted. To add a password, look for a Password field in the settings and type a strong password you will not remember easily.
Using Firefox's Restricted Profiles for family devices
If you are setting up Firefox for a child or managing a shared family computer, Restricted Profiles offer a simpler approach than extensions. Open Firefox and click the three horizontal lines (menu button) in the top right corner. Scroll down and click Settings.
On the left side, click Privacy & Security. Scroll down to the section called Restrictions. You will see options to block adult content, gambling sites, violence, and other categories. Check the boxes next to the categories you want to block.
When you turn on Restricted Profiles, Firefox will ask you to set a password. This password prevents anyone using the profile from turning off the restrictions. Write down this password somewhere safe — if you lose it, you will need to reset Firefox to change the settings.
What happens when you try to visit a blocked site
When you attempt to reach a blocked website, Firefox will not load the page. Instead, you will see a message from the blocking extension or from Restricted Profiles explaining that the site is blocked. The message usually includes a reason — for example, "This site is blocked by LeechBlock NG."
If the extension has a password, you might see an option to temporarily unblock the site, but it will ask for the password. If you set the block to be active only during certain hours, the message will tell you when the block will turn off. Outside those hours, the site will load normally.
Blocking only affects Firefox on that computer. If you open the same website in Chrome, Safari, or another browser, it will load normally. The block does not affect your phone or other devices unless you set up blocking there separately.
Removing or changing blocked websites
To unblock a website, open the blocking extension's settings again. Find the site in the list of blocked addresses and click the Remove or Delete button next to it. The site is now unblocked and you can visit it again.
If you want to block additional sites, click Add in the extension settings, type the new address, and click Add again. You can block as many sites as you need. Most extensions let you block hundreds of addresses without slowing down Firefox.
If you change your mind about using a blocking extension entirely, you can remove it from Firefox. Click the menu button (three lines) in the top right, go to Add-ons, find the extension in the list, and click Remove. Firefox will ask you to confirm — click Remove again. The extension is uninstalled and all blocks are turned off when ready.
Choosing between extensions and Restricted Profiles
Use a blocking extension if you want to block specific websites, set times when the block is active, or password-protect your settings. Extensions give you the most control and work well if you are trying to limit your own browsing habits.
Use Restricted Profiles if you are managing Firefox for a child or someone else and want to block entire categories of content rather than individual sites. Restricted Profiles are simpler to set up and do not require installing anything extra. They are built into Firefox and work when ready.
If you want both — blocking specific sites and categories — you can use an extension and Restricted Profiles together. The blocks will stack, so a site has to pass both filters to load.
Frequently Asked Questions
Can someone turn off the block if they know the website address?
No, if you set a password on the blocking extension or Restricted Profiles, they cannot turn off the block without entering the password. This is the main reason to add a password — it prevents you or someone else from disabling the block on impulse. Choose a password you will not guess easily.
Will blocking a website in Firefox block it on my phone too?
No. Blocking only affects Firefox on that specific computer. Your phone, tablet, and other devices are not affected. If you want to block sites on your phone, you will need to set up blocking separately in your phone's browser or use a different tool designed for mobile devices.
What if I block a site by accident and cannot remember the password?
If you set a password on a blocking extension, you will need to uninstall the extension to remove the block. Click the menu button, go to Add-ons, find the extension, and click Remove. If you set a password on Restricted Profiles, you will need to reset Firefox, which erases your bookmarks and settings. Write down your password somewhere safe to avoid this.
Do blocking extensions slow down Firefox?
No, most blocking extensions like LeechBlock NG use very little computer power and do not noticeably slow down Firefox. They run in the background and only check websites against your blocked list when you try to visit them. You should not see any difference in browsing speed.
Can I block a website only on certain days of the week?
Yes, most blocking extensions let you set a schedule by day and time. For example, you can block a site Monday through Friday from 9 AM to 5 PM but allow it on weekends. Open the extension settings and look for a section called Times or Schedule to set this up.