UBlock Origin

uBlock Origin (previously uBlock and originally μBlock) is a free and open-source browser extension for content filtering, including ad blocking. The extension is available for Chrome, Chromium, Edge, Firefox, Brave, Opera, Pale Moon, as well as versions of Safari before 13. uBlock Origin has received praise from technology websites and is reported to be much less memory-intensive than other extensions with similar functionality. uBlock Origin's stated purpose is to give users the means to enforce their own (content-filtering) choices.

uBlock Origin is actively developed and maintained by its creator and lead developer Raymond Hill.

uBlock
uBlock was initially named "μBlock" but the name was later changed to "uBlock" to avoid confusion as to how the Greek letter μ (Mu/Micro) in "μBlock" should be pronounced. Development started by forking from the codebase of HTTP Switchboard along with another blocking extension called uMatrix, designed for advanced users. uBlock was developed by Raymond Hill to use community-maintained block lists, while adding features and raising the code quality to release standards. First released in June 2014 as a Chrome and Opera extension, in 2015 the extension became available in other browsers.

A joint Sourcepoint and comScore survey reported an 833% growth from November 2014 to August 2015, the strongest growth among adblockers listed. The report attributed the growth to the desire of users for pure blockers, outside the "acceptable ads" program operated by Adblock Plus.

On April 3, 2015, Hill transferred the uBlock project to Chris Aljoudi due to frustrations with dealing with requests as the project's popularity increased. "These projects are to me, not a full time job. It stopped being a hobby when it felt more and more like a tedious job. I will keep maintaining my version (and share with whoever care to use it) because it guarantees the tool will match what I want out of it." Hill created his own fork and renamed it uBlock Origin on April 6.

Since October 2017, uBlock Origin has been completely separated from Aljoudi's uBlock. Aljoudi created ublock.org to host and promote uBlock and to request donations. In response, uBlock's founder Raymond Hill stated that "the donations sought by ublock.org are not benefiting any of those who contributed most to create uBlock Origin." The development of uBlock stopped in August 2015 but there were sporadic updates from January 2017.

In July 2018, ublock.org was acquired by AdBlock and resumed development. From February 2019, uBlock began allowing users to participate in "acceptable ads", a program run by Adblock Plus that allows some ads deemed "acceptable" and nonintrusive, and for which larger publishers pay a fee.

uBlock Origin
uBlock Origin remains independent and does not allow ads for payment. The project refuses donations and instead advises supporters to donate to maintainers of block lists. Hill continued to work on the extension under the name uBlock Origin, abbreviated as uBO and originally as uBlock0.

In January 2016, uBlock Origin was added to the repositories for Debian 9 and Ubuntu 16.04. The extension was awarded "Pick of the Month" by Mozilla for May 2016.

On December 11, 2016, Nik Rolls released a fork of uBlock Origin for the Microsoft Edge browser (now known as Microsoft Edge Legacy). In April 2020, this fork was deprecated as Microsoft replaced Microsoft Edge Legacy with a Chromium-based Edge.

, the uBlock Origin Chrome extension had over 37 million active users and the Firefox version had over 7 million active users.

Blocking and filtering
uBlock Origin supports the majority of Adblock Plus's filter syntax. The popular filter lists EasyList and EasyPrivacy are enabled by default. The extensions are capable of importing hosts files and a number of community-maintained lists are available at installation. Among the host files available, Peter Lowe's ad servers & tracking list and lists of malware domains are also enabled as default. Some additional features include dynamic filtering of scripts and iframes and a tool for webpage element hiding.

uBlock Origin includes a growing list of features not available in uBlock, including:
 * A mode to assist those with color vision deficiency.
 * A dynamic URL filtering feature.
 * Logging functionality.
 * Interface enhancements including a DOM inspector, privacy-oriented options to block link prefetching, hyperlink auditing, and IP address leaks via WebRTC (this feature was removed in version 1.38 on all platforms except Android, as most browsers are no longer vulnerable ).

Site-specific switches to toggle the blocking of pop-ups, strict domain blocking, cosmetic filtering, blocking remote fonts, and JavaScript disabling were also added to uBlock Origin. The Firefox version of uBlock Origin has an extra feature which helps to foil attempts by web sites to circumvent blockers.

CNAME-uncloaking third-party trackers in Firefox
In November 2019, a uBlock Origin user reported a novel technique used by some sites to bypass third-party tracker blocking. These sites link to URLs that are sub-domains of the page's domain, but those sub-domains resolve to third-party hosts via a CNAME record. Since the initial URL contained a sub-domain of the current page, it was interpreted by browsers as a first-party request and so was allowed by the filtering rules in uBlock Origin (and in similar extensions). The uBlock Origin developer came up with a solution using a DNS API which is exclusive to Firefox 60+. The new feature was implemented in uBlock Origin 1.25, released on February 19, 2020.

Performance
Technology websites and user reviews for uBlock Origin have regarded the extension as less resource-intensive than extensions that provide similar feature sets such as Adblock Plus. A benchmark test, conducted in August 2015 with ten blocking extensions, showed uBlock Origin as the most resource-efficient among the extensions tested.

uBlock Origin surveys what style resources are required for an individual web page rather than relying on a universal style sheet. The extension takes a snapshot of the filters the user has enabled, which contributes to accelerated browser start-up speed when compared to retrieving filters from cache every time.

Limitations in Chromium-based browsers
In 2023, Google made changes known as "Manifest V3" to the WebRequest API used by ad blocking and privacy extensions to block and modify network connections. Following Google's implementation of Manifest V3 and the end of support for V2, uBlock Origin's effectiveness is drastically reduced in Google Chrome and other Chromium-based browsers. The alternative 'uBlock Origin Lite' for Chromium browsers lacks filter list updates outside of extension updates, and has no custom filters, strict-blocked pages, per-site switches, or dynamic filtering. Non-Chromium browsers such as Firefox are unaffected. Google has been criticized for implementing some of these features due to its domination in the online advertising market.

Supported platforms
uBlock Origin is actively developed for applications based on two major layout engines.

Currently supported

 * Blink
 * Google Chrome/Chromium (desktop)
 * Brave (desktop)
 * Opera (desktop)
 * Microsoft Edge (Chromium) (desktop)
 * Kiwi (mobile)
 * Gecko
 * Firefox (desktop: 0.85.5 and later)
 * Firefox for Android (mobile: 0.9.1.0 and later)
 * Thunderbird (desktop: 1.3.0 and later)
 * SeaMonkey

Previously supported

 * WebKit
 * Safari (desktop: uBlock Origin 1.10.0 and later (Beta)). Stopped working with macOS 10.15 Catalina and Safari 13.
 * EdgeHTML
 * Microsoft Edge (legacy) (uBlock Origin is available on the Windows Store in beta from 1.10.0).