uBlock Origin for Firefox: Install, Settings and What It Blocks

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Here is the short version of what this guide walks through:

1. Find uBlock Origin on the Firefox Add-ons site and add it.
2. Confirm it is running from the toolbar icon.
3. Check the default filter lists it turns on.
4. Adjust a few settings only if you need to.
5. Turn it off for a site that will not load properly.
6. Test what it blocks on a page you visit often.
7. Know where it stops, such as with video ads inside some players.

If you have been dealing with pages full of video ads, pop-ups and autoplay, you know how much that gets in the way of reading or watching. Ads also slow pages down and can use up data on a phone connection. Many people switch browsers and then wonder whether their blocker will follow them. Your blocker may not carry over, so check before you assume it will.

This page covers the uBlock Origin extension on desktop Firefox: how to install it, what its settings do, and what it blocks by default. You do not need to be technical to follow along. Each step is short, and you can stop after the install if the defaults suit you.

Why uBlock Origin Works in Firefox

Firefox runs extensions, and uBlock Origin is one you can install straight from the official Firefox Add-ons site at addons.mozilla.org. Search for "ublock origin" there, check that the listing is published by the developer, and click "Add to Firefox." That is the safe route. Avoid third-party download sites.

Firefox still supports the full version of the extension, and that is the main reason many users choose it. The full version can use advanced filtering, so it can block more than the simpler tools that come with some browsers. For most users, that means fewer ads, fewer pop-ups and less tracking across the web.

Is it the same as other blockers with similar names?

Not always. Several products use names like "uBlock," "Adblock" or "Ad Block," and they are not the same thing. Some are built by different developers and work differently. Before you install, look at the developer name on the add-on page. If you want the uBlock Origin described here, the listing should say so clearly.

If you are unsure which blocker to pick, the other pages in this hub compare them side by side.

How to Install uBlock Origin on Firefox

Installing uBlock Origin takes about a minute. It is free, and you do not need an account. The steps below work on Firefox for desktop.

1. Open the Firefox Add-ons site at addons.mozilla.org and search for "uBlock Origin."
2. Check the publisher before you install. The listing should show the uBlock Origin developer, not a similar-sounding name. Plain Ad Blockers is the name this page uses for the blocker it covers, so treat any other publisher with suspicion.
3. Click "Add to Firefox." A permissions prompt appears. Read it, then click "Add" to confirm.
4. Look for the shield-style icon in the toolbar. If you do not see it, click the puzzle-piece extensions menu and pin uBlock Origin so it stays visible.
5. Reload any tabs that were already open. Blocking applies to pages as they load, so a refresh makes sure the ads on those pages are caught.

Does it work out of the box?

For most users, yes. The default settings block a large share of ads, pop-ups and trackers without any changes. Click the icon to see how many items were blocked on the current page. You only need to open the settings if a site breaks, and you can turn blocking off for that one site from the same panel.

Default Settings and What They Do

When you first install uBlock Origin on Firefox, it works straight away. You do not need to change anything. The defaults are set to balance blocking with keeping websites working, and for most everyday browsing they are the right choice.

What are the filter lists?

Filter lists are the rules uBlock Origin uses to decide what to block. Each list is a long catalogue of known ad and tracking domains, maintained by volunteers and groups who track them. By default, the lists for ads and trackers are switched on, along with a few for malware and annoyances.

To see them, open the uBlock Origin icon in the Firefox toolbar, click the settings gear, and choose the Filter lists tab. You can see which lists are active and when they were last updated. Leave them on unless you have a specific reason to change them.

What is cosmetic filtering?

Some ads are not loaded from a blocked address, so network blocking alone misses them. Cosmetic filtering hides the leftover boxes and page elements, like empty ad slots or sponsored panels. It is on by default and works quietly in the background.

What about dynamic filtering and advanced mode?

Dynamic filtering and advanced mode are off by default. They give you fine control over which requests each site may make, through a grid in the popup. That is useful if you want to tune things closely, but it is also easy to break a page with it. If you only want ads and trackers gone, leave both off.

Most readers will find the defaults do what they need. Keep them unless a particular site gives you trouble, and then turn off blocking for that one site only.

What uBlock Origin Blocks and What It Cannot

uBlock Origin is a free extension for Firefox, and it does its main job well. It blocks display ads, pop-up windows and the known tracking scripts that follow you from site to site. Most of that happens quietly, so you usually just notice that pages load faster and look cleaner.

It also blocks many known malicious and scam domains. It does this through its filter lists, which are regularly updated lists of addresses known to host ads, trackers or dangerous content. This is not the same as full antivirus protection, but it does stop a fair number of bad sites before they load.

Will it block every ad?

No, and it helps to know the limits before you install it. You may still see:

• Ads served from the same site as the content you are reading, which are hard to separate from the page itself
• Some YouTube ads, since YouTube serves its ads from the same place as its videos. The YouTube page covers your options and the limits in more detail.

Does it work outside Firefox?

Only inside Firefox. uBlock Origin does not cover other apps on your device, so a game or a desktop app showing ads will not be affected.

Benefits and limits at a glance

Turning It Off for a Site and Fixing Breakage

Sometimes a page or a video player will not load properly with uBlock Origin running. A login form stays blank, a video refuses to play, or a checkout button does nothing. This is usually the blocker stopping something the site needs, and you can fix it without removing the extension.

The quickest fix is to pause blocking for that one site:

1. Open the site that is misbehaving.
2. Click the uBlock Origin icon in the Firefox toolbar.
3. Click the large power button in the popup. This turns blocking off for that site only.
4. Reload the page and check whether it works now.
5. When you are done, open the popup again and turn blocking back on for the site.

If the site still breaks after you pause blocking, it may be detecting blockers and refusing to work with them. In that case you can add the site to your trusted list so the blocker leaves it alone. Use this only for sites you actually trust, since an exception means ads and trackers there will load as normal.

For more detail, see how to turn off an ad blocker for one site in Firefox. The same toolbar popup shows what was blocked on the page, which helps you spot which filter is causing the trouble.

Is It Safe, Free and Worth Using?

uBlock Origin is free and open source. There is no paid version, no paywall and no upgrade prompt pushing you toward a subscription. The code is public, so anyone can check what it does.

Still, it is worth a quick check before you install any extension. Here is what to do:

1. Install it only from the official add-ons site, addons.mozilla.org. Avoid download links from random sites.
2. Read the permissions list the install prompt shows. A blocker needs to read and change data on the sites you visit, so that permission is expected. Be wary of anything asking for more than that.
3. Check the publisher. The Firefox listing shows who published the add-on.

Some people compare uBlock Origin with Adblock Plus. The main difference is that Adblock Plus has an acceptable ads program turned on by default. That lets some companies pay to get their ads past the block lists. You can switch it off in settings, but you have to know to do it. If you want the full picture, see our page on Adblock Plus on Firefox.

uBlock Origin also works in Firefox for Android, since Firefox for Android supports extensions. For the phone setup, see Firefox for Android ad blocking.

Frequently asked questions