Pale Moon is a free, open-source web browser for Windows, macOS and Linux, with beta builds for FreeBSD and community-made packages for other systems. It descends from Mozilla Firefox code but is developed independently, with its own rendering engine, release plan and interface. The project targets people who want to reshape a browser with deep add-ons, keep the classic menu-and-toolbar layout and avoid telemetry.
Goanna engine and the UXP platform
Pale Moon draws web pages with Goanna, a layout and rendering engine forked from Gecko. Goanna runs inside UXP (Unified XUL Platform). Goanna has diverged from Gecko and does not behave exactly like it.
The engine follows HTML and CSS specifications closely and supports extended HTML5, CSS3 and DOM features, SVG, Canvas and downloadable web fonts. Image support covers JPEG, JPEG-XL, PNG, WebP and GIF, but not AVIF. The browser deliberately leaves out some draft standards and newer APIs. As a result, certain websites built for Chromium or current Firefox may not work fully in Pale Moon.
Pale Moon also keeps everything in a single process instead of splitting tabs into separate processes. The project’s reasoning is that this lowers memory use and reduces the attack surface.
XUL extensions, themes and legacy plugins
Extensibility is the main reason many users choose Pale Moon. Its add-ons are written in XUL and have low-level access to the browser. This access lets an extension change core behavior and rebuild parts of the interface rather than only add a toolbar button or react to page content. Many older Firefox extensions from before the Australis redesign still run, although they are not guaranteed to work. They receive support only if the community maintains them.
Pale Moon has its own add-ons site with extensions, themes, search plugins and language packs. Pale Moon supports two kinds of visual themes: lightweight Personas that change background images and colors, and complete themes that restyle every part of the browser window.
Unlike most current browsers, Pale Moon still loads NPAPI plugins such as Java, Flash and Silverlight. That matters for old web applications and intranet tools that still depend on them.
Classic interface and customization
The Pale Moon window looks and works much like Firefox did before its Australis and Photon redesigns. Users can rearrange toolbars, menus and the tab strip through the Customize dialog. The browser also includes a padlock indicator that shows connection status in the frame. A graphical tab switcher includes quick search.
The standard preferences go further than in mainstream browsers, with options for tab behavior, image loading, security and smooth scrolling. For settings that would otherwise mean editing values in about:config, the Pale Moon Commander extension adds an “Advanced Options” window to the Options and Tools menus.
Tab Groups, which sorts open tabs into named sets, was moved out of the core into an optional extension that restores its shortcuts and menus.
Privacy defaults and security model
Pale Moon contains no advertising, telemetry or data collection. DuckDuckGo is the default search engine. Users can change both the search engine and the start page.
Pale Moon gets regular security patches and shows site identity and security levels in the interface. It also includes an active filter against cross-site scripting (XSS). The browser does not use QUIC or 0-RTT connection resumption, which the developers avoid for security reasons.
Several Firefox components are disabled or removed altogether: WebRTC, built-in DRM for protected video, the integrated PDF reader, parental controls and silent background updates through a Windows service. Browser-based video calls and DRM-protected streaming services are therefore not available.
Pale Moon Sync
Pale Moon has its own sync service, separate from Firefox Sync and not compatible with it. However, the project currently lists the service as offline for security reasons. After signing in with an email address and password, users choose what to synchronize: bookmarks, open tabs, browsing history, form history, passwords and a limited set of preferences. The browser encrypts data before upload, and only the personal recovery key kept in the browser can decrypt it. The key never reaches the server.
The service also works between Pale Moon installations on different operating systems. It is not meant as a backup. The server prunes data regularly, and losing the recovery key means the stored data has to be deleted. Users who want full control can run their own Sync server.
Portable edition and profile backups
Pale Moon Portable for Windows runs from a USB stick or another writable drive. Bookmarks, passwords, history and downloads stay on that drive instead of on the host computer. The portable build does not integrate with the desktop. It cannot run from read-only media such as DVDs.
For installed copies on Windows, a separate Pale Moon Profile Backup tool saves and restores a whole profile, including settings, data and customizations. It offers basic compression options. It works only with the default profile location, and its backups are neither encrypted nor password-protected. Users can back up a portable installation by copying its folder.
