uBlock Origin is a CPU- and memory-efficient, wide-spectrum content blocker for Chromium and Firefox, aimed at anyone who wants ads, trackers, coin miners, popups, anti-blockers and malware sites neutralised by default without hand-tuning anything.

What it is

uBlock Origin, commonly shortened to uBO, is an open-source browser extension written in JavaScript and released under the GPL-3.0 licence. It lives in the browser-extension ecosystem, shipping against the Chromium and Firefox extension platforms as well as the Thunderbird add-on system. Its stated primary goal is to help users neutralise privacy-invading methods in a way that welcomes users who do not wish to use more technical means, and it pursues that goal through a combination of preselected filter lists and an optional advanced interface for people who do want fine-grained control.

The concrete problem it solves is the layer of advertising, tracking, coin-mining, popup and anti-blocker machinery that loads in a browser before any extension intervenes. It replaces the unblocked default behaviour of the browser itself, and it occupies the position in the extension bar that a blocker such as Adblock Plus would otherwise hold. Out of the box it subscribes to EasyList, EasyPrivacy, Peter Lowe's Blocklist, the Online Malicious URL Blocklist and uBO filter lists, and it also accepts hosts files. It uses the EasyList filter syntax and extends that syntax so custom rules and filters remain expressible.

Key capabilities

• Wide-spectrum blocking enabled by default through EasyList, EasyPrivacy, Peter Lowe's Blocklist, the Online Malicious URL Blocklist and uBO filter lists.
• EasyList filter syntax with extended syntax for custom rules, plus support for hosts files.
• Two interfaces: Basic Mode for an install-it-and-forget-it setup configured optimally by default, and Advanced Mode with a point-and-click firewall configurable on a per-site basis.
• Any preselected filter list can be unselected if the user judges that uBO blocks too much.
• Packages published for Firefox Add-ons (desktop and Android), Edge Add-ons, Opera Add-ons, Thunderbird Add-ons and GitHub Releases.
• GitHub Releases carries stable and development builds for Firefox, Chromium MV2 and Thunderbird, alongside the related uBlock Origin Lite project.
• Translations are managed through Crowdin, and an Enterprise Deployment path is documented alongside Installation and Release History.

Who uses it and how

• Firefox users on desktop and Android, where the project states uBO works best.
• Chromium-based browser users, since uBO should be compatible with any Chromium-based browser and is published on the Edge and Opera add-on stores.
• Thunderbird users who want blocking applied to feeds; in Thunderbird it does not affect emails, only feeds.
• Organisations with managed fleets, served by the documented Enterprise Deployment route.
• Users who need per-site control, handled through the Advanced Mode firewall rather than blanket lists.

Getting started

Install from Firefox Add-ons, Edge Add-ons, Opera Add-ons or Thunderbird Add-ons. For Chromium MV2, Thunderbird beyond 1.49.2, and development builds, download from GitHub Releases and place the extension manually into the browser.

How it compares

Among blockers named in the project's own material, Adblock Plus installs with only EasyList, ABP filters and Acceptable Ads enabled by default, whereas uBO enables a broader set of lists from the start. The related uBlock Origin Lite is published alongside it as a separate project. The project also warns that uBO performs as well as or better than competing blockers only when it is not run in combination with them.

When to use it — and when not

Firefox is the best-supported target, and Chromium users should note that Manifest V2 is on the way out: Chrome Web Store distribution removed on 2026-08-31, Microsoft Edge beginning its consumer MV3 transition in August 2026 with the consumer move complete by the end of 2026 and enterprise deprecation following in early 2027. Thunderbird add-on distribution is stuck at 1.49.2 and later versions must come from GitHub Releases, and the Chromium and Thunderbird builds placed manually usually will not auto-update, so someone must track releases by hand. Do not run uBO alongside another content blocker, and anyone unwilling to manage manual installs or to accept the MV2 transition should not pick it.