Pale Moon

Pale Moon is a free and open-source web browser licensed under the MPL-2.0 with an emphasis on customization. Its motto is "Your browser, Your way." There are official releases for Microsoft Windows, FreeBSD, macOS, and Linux.

Pale Moon originated as a fork of Firefox, but has subsequently diverged. The main differences are the user interface, add-on support, and running in single-process mode. Pale Moon retains the user interface of Firefox from versions 4 to 28 and supports legacy Firefox add-ons.

Features
Pale Moon's default user interface is the one that was used by Firefox from versions 4 to 28, known as Strata. It always runs in single process mode and uses a rendering engine known as Goanna. The browser has its own set of extensions and supports legacy Firefox add-ons built with XUL and XPCOM, which Firefox dropped support for. NPAPI plugins are also supported. The browser's entire user interface can be customized by complete themes and lightweight themes are also available. Pale Moon's default search engine is DuckDuckGo and it uses the IP-API service instead of Google for geolocation. The browser is known to be lightweight on resource usage.

Pale Moon has no telemetry or data collection.

Unified XUL Platform (UXP)
Pale Moon is built upon the Unified XUL Platform (UXP), a cross-platform, multimedia application base that was forked from Mozilla code prior to the introduction of Firefox Quantum. UXP is a fork of the Firefox 52 ESR platform that was created in 2017 due to XUL/XPCOM support being removed from the Firefox codebase. It includes the Goanna layout and rendering engine, a fork of Mozilla's Gecko engine. Moonchild Productions develops UXP independently alongside Pale Moon.

Supported platforms
Windows 7 SP1 and above are supported, along with any modern Linux distribution as long as the processors support SSE2 and there is at least 1 GB of RAM. macOS on Intel and ARM processors is supported. FreeBSD is also supported.

Previously, Windows XP and Vista were supported, but are no longer supported from versions 27 and 28  onward, respectively.

An Android build was developed in 2014 but was cancelled by the developer due to lack of community involvement a year later.

History
Pale Moon was created and is primarily maintained by one developer, M.C. Straver. Prior to version 26, Pale Moon used the same rendering engine as Firefox, known as Gecko. With version 26 in 2016, Pale Moon switched to using the Goanna rendering engine, a fork of Gecko. In 2017, the Pale Moon team began the Unified XUL Platform due to upcoming changes in the Mozilla codebase. The Basilisk web browser was developed to serve as a "reference application" for development before Pale Moon switched over to using it.

In 2019, hackers breached a Pale Moon archive server and infected the older installers with malware; then-current Pale Moon releases were not affected. The breach took place between April and June, and the affected server was taken down on July 9 when it was discovered.

In 2022, a change in direction for Pale Moon was announced to improve website and add-on capability. This resulted in version 30, which used the Firefox GUID to improve compatibility with legacy Firefox extensions and started increased development of UXP and Goanna. A few days later, version 30 had to be recalled due to one of the developers causing issues before exiting the project, such as messing up the add-ons server. Version 31 was issued in response to fix these issues.

Notable forks
MyPal was formerly a fork of Pale Moon that supported Windows XP, but after issues with the lead developer of Pale Moon regarding licensing, it was rebased on Firefox Quantum. Versions of MyPal afterwards are a fork of the Firefox 68 codebase.

New Moon is another fork of Pale Moon which supports Windows XP.