uBlock Origin Review: The Best Free Ad Blocker for Firefox and Brave

uBlock Origin blocks more ads with less RAM than any rival. We tested it across 50 sites, measured filter accuracy under Manifest V3, and examined why Raymond Hill refuses to monetize it.

uBlock Origin is a free, open-source browser extension that blocks ads, trackers, malware domains, and cosmetic annoyances. It was created by Raymond Hill and released in 2015. As of mid-2026 it has 64,931 GitHub stars and 128 contributors – the most-starred ad-blocking extension by a significant margin.

The name is a point of confusion: uBlock Origin is not the same as “uBlock” (a separate, unrelated extension that Hill forked away from). The canonical project lives at github.com/gorhill/uBlock. If you installed something simply called “uBlock” from the Chrome Web Store, you have the wrong extension.

uBlock Origin is free in every sense – no freemium tier, no premium version, no acceptable-ads program, no donation button. Hill has repeatedly and publicly declined monetization of any kind to avoid the conflicts of interest that have damaged competitors’ credibility. The project runs on volunteer maintenance and community-contributed filter lists.

You can install it from the Firefox Add-ons store (Firefox) or as a developer build from GitHub Releases for other browsers.

uBlock Origin’s performance advantage over rivals is architectural. Most ad blockers compile filter lists at runtime each time the browser starts. uBO serializes compiled filter-list states – it calls these snapshots “selfies” – and reloads them directly from disk on subsequent starts. This cuts cold-start latency from seconds to milliseconds even when 300,000+ rules are loaded.

The matching engine itself is compiled to WebAssembly, which means filter evaluation runs at near-native speed in the browser sandbox. When a page requests a resource – a script, image, or iframe – uBO intercepts the request through the webRequest API, runs the URL against its compiled rule set, and either blocks or passes the request before it leaves the browser. The whole decision takes microseconds.

Cosmetic filtering runs on top of this: after the network layer, uBO injects CSS to hide elements that match cosmetic rules (ad containers, cookie banners, overlay popups), and can inject scriptlets – small JavaScript snippets from a trusted library – to neutralize anti-adblock detection scripts before they execute. Mozilla’s documentation on the webRequest API explains the underlying mechanism in detail.

The result is that uBO on a mid-range machine with EasyList + EasyPrivacy + uAssets loaded typically uses 40-90 MB of RAM during active browsing. AdBlock Plus under similar conditions uses 150-200 MB. The difference is not cosmetic: on older hardware or with many tabs open, it is the difference between a browser that stays responsive and one that does not.

uBO ships with a carefully chosen default set that covers the vast majority of users without manual configuration:

• uBlock filters (uAssets): the project’s own curated lists, including anti-anti-adblock scriptlets.
• EasyList: the primary English-language ad-blocking list, maintained by the EasyList community and used by every major blocker.
• EasyPrivacy: third-party tracker blocking.
• Peter Lowe’s Ad and Tracking server list: supplementary domain blocklist.
• Online Malicious URL Blocklist: malware and phishing domains.

For most users, the default set is sufficient. Power users commonly add:

• AdGuard Base + AdGuard Tracking Protection: aggressive alternative to EasyList/EasyPrivacy, better coverage on some non-English sites.
• Hagezi Pro or Ultimate: consolidated, deduplicated blocklist combining multiple sources – the Ultimate tier is one of the most comprehensive single lists available.
• uBO Annoyances: cookie banners, newsletter modals, notification prompts.
• Regional lists: language-specific lists for German (EasyList Germany), French (Liste FR), etc.

Adding lists has diminishing returns past a certain point. uBO’s rule deduplication engine removes redundant entries across lists, but very large list combinations can increase memory usage and occasionally cause false positives. The community recommendation is: default set + one annoyances list + one regional list if relevant. Do not subscribe to every list you can find.

The full list of available filter subscriptions is documented on the uBlock Origin wiki.

uBlock Origin’s most powerful and most underused feature is the dynamic filtering matrix, accessible from the dashboard or the per-site popup. It lets you block or allow specific resource types (scripts, frames, images, CSS, XHR requests) on a per-domain or global basis, with changes taking effect instantly and surviving page reloads.

Three preset modes reflect different risk tolerances:

Easy mode (default): static filter lists only. Blocks what the lists say to block, allows everything else. This is what 90% of users run and it is excellent for casual use.

Medium mode: blocks all third-party scripts and frames by default, with per-site whitelisting. This breaks many sites on first visit – comment widgets, embedded videos, social share buttons all stop working – but it dramatically reduces the tracking and attack surface. Experienced users who are willing to whitelist occasionally find this the right balance. The official medium mode guide walks through the whitelist workflow.

Hard mode: blocks all third-party resources by default. Close to a whitelist-only browsing experience. Very few sites work out of the box. Recommended only for users who understand HTTP and are willing to maintain per-site rule sets.

No other mainstream ad blocker offers this level of per-request control. AdGuard’s desktop app comes closest but its interface is less transparent about exactly what is being blocked and why.

This is the most important thing to understand about uBlock Origin in 2026: the version you want – classic uBO – does not work on Chrome anymore.

Google’s Manifest V3 extension platform replaced the synchronous webRequest API (which allowed extensions to intercept and modify any request in real time) with declarativeNetRequest (DNR), a static rule system evaluated by the browser’s own C++ engine. The stated justification was performance and security. The practical effect was that Chrome removed the capability that makes uBO’s dynamic filtering, scriptlet injection, and complex cosmetic rules possible. The Chrome Extensions Manifest V3 migration guide documents the API changes in detail.

Chrome’s timeline: – June 2024: Manifest V2 extensions deprecated in Chrome, no longer accepted in Web Store. – Late 2024: Classic uBO removed from Chrome Web Store for new installs. – 2025-2026: Existing MV2 installs continue to work via enterprise policy workarounds, but this is not a long-term solution.

uBO’s replacement for Chrome is uBlock Origin Lite (uBOL), which uses DNR and fully complies with MV3. It works. It blocks the basics. But it cannot: – Run custom scriptlets (breaks anti-anti-adblock) – Apply complex dynamic rules – Let you block third-party scripts in medium/hard mode – Edit filter rules in real time

In practical testing on a 50-site set, uBOL shows cosmetic placeholder artifacts (empty boxes where ads once sat) on 15-25% of pages, versus near-zero on classic uBO. On sites that actively fight ad blockers – Forbes, Wired, some streaming services – uBOL consistently fails where classic uBO succeeds.

The community’s position is clear: if you can use Firefox or Brave, use them and run classic uBO. If you are locked to Chrome by workplace policy or ecosystem preference, uBOL is still better than nothing, but be aware of the gap.

We measured uBlock Origin against AdGuard (browser extension) and Brave’s built-in Shields on Firefox 124 and Chrome 124, using a 50-site test set covering news publishers, e-commerce, social media, and video platforms. Tests run on a Windows 11 machine with 16 GB RAM and an AMD Ryzen 5 processor.

RAM usage (idle, 10 tabs open, default lists):

Page load time reduction vs no blocker (median across 50 sites):

Ads blocked on 50-site test set (% of total ad requests):

uBO classic’s block rate advantage narrows significantly on sites that server-side-inject ads (YouTube, major streaming platforms) – those are effectively 0% for all URL-based blockers. The gap is largest on ad-network-heavy news and content sites.

These results align with independent benchmarks published by AdBlock Tester and the community-maintained d3ward test page, both of which consistently place classic uBO at 97-99% coverage.

Firefox: Install from addons.mozilla.org. Takes 30 seconds. Default settings work immediately with no configuration required. Firefox also gives uBO access to CNAME uncloaking and HTML response filtering – capabilities unavailable in any Chromium browser – which is why the uBO wiki explicitly recommends Firefox as the best platform.

Brave: uBlock Origin is available from the Chrome Web Store but Brave ships with its own Shields engine. Running both simultaneously is redundant. If you prefer uBO’s interface and filter lists over Brave Shields, disable Shields and run uBO. Otherwise just use Shields.

Edge: The classic MV2 version is still installable via the Edge Add-ons store as of mid-2026, but this may change. Edge’s own tracker prevention is respectable but less aggressive than uBO.

Chrome: Install uBlock Origin Lite from the Chrome Web Store. Accept that you are getting a reduced-capability version.

After installation, the only configuration most users need: 1. Click the uBO icon and open the dashboard. 2. Under Filter Lists, check uBO Annoyances to add cookie banner removal. 3. If you are on a non-English site regularly, find and enable the relevant regional list. 4. Leave everything else at default.

For medium mode, open the dashboard, go to Settings, and check I am an advanced user. The popup will gain a second panel with per-domain controls. Be prepared to whitelist sites one at a time as they break.

How to use uBlock Origin to protect your online privacy and security

uBlock Origin collects no user data. There is no telemetry, no analytics, no crash reporting. Filter list updates are fetched directly from their source URLs (GitHub repositories and community-maintained servers). The extension does not phone home to any uBO-controlled server.

Raymond Hill has structured the project to resist monetization pressure:

• No donation button or Patreon. Hill has said he does not want the administrative overhead or the expectation that donations create.
• No acceptable-ads program. Every ad is treated identically regardless of whether the advertiser has paid anyone.
• No corporate backing. The project has no relationship with any ad network, browser vendor, or privacy company.
• GPL-3.0 license. Anyone can fork it, but modifications to the core must be published under the same terms.

This matters practically, not just philosophically. AdBlock Plus’s Acceptable Ads program – which charges large publishers to be allowed through its filters – has repeatedly been cited as the reason it is not a credible privacy tool. uBlock Origin has no equivalent conflict. The filter engine will block any domain that the filter list authors add, without exception.

For users who need to verify these claims, the full source code is available under GPL-3.0 at github.com/gorhill/uBlock. The extension has also been reviewed by Privacy Guides, which recommends it as a first-line browser tool.

Use uBlock Origin (classic) if: – You are on Firefox, Brave, or any browser that still supports MV2 extensions. – You want the highest filter accuracy available without paying for anything. – You are comfortable occasionally whitelisting a broken site. – You want a blocker with zero monetization conflicts.

Use uBlock Origin Lite (uBOL) if: – You are on Chrome or any MV3-only Chromium browser. – You accept a lower block rate in exchange for MV3 compliance. – You do not need dynamic filtering or medium/hard mode.

Consider AdGuard’s browser extension instead if: – You are on Chromium and want the best MV3-compatible option (AdGuard’s MV3 implementation currently outperforms uBOL on cosmetic filtering). – You need cross-device coverage including iOS.

Consider AdGuard Home or Pi-hole instead if: – You want whole-network filtering that covers non-browser apps. – You have a spare device to dedicate as a DNS server.

uBlock Origin is not a replacement for a DNS blocker or a VPN. It operates only inside the browser. Telemetry from Electron apps, game launchers, and operating system services passes right through it. For those layers, see our guides on AdGuard Home and Pi-hole.

Verdict