Basilisk Web Browser
TL;DR
Basilisk is a free, open-source web browser that serves as a "what if" project and development testbed for the team behind the Pale Moon browser.
What is Basilisk
Basilisk is a free, open-source web browser built by a team originally associated with the Pale Moon project.
It uses the Goanna rendering engine (a fork of Mozilla’s Gecko engine) and is built on the Unified XUL Platform (UXP).
One of its goals is to preserve and support technologies and features that Mozilla Firefox dropped (from version 57 onward) — especially the old-style UI, classic extensions (XUL/XPCOM), NPAPI plugin support, etc.
Timeline & Key Events
Date—>Event / Change
2017—>Announcement & First Version_: Basilisk was first announced by M.C. Straver (lead of Pale Moon) in 2017. It was intended as a “reference application for development of the XUL platform.”
November 2017—>First public version released.
April 2018—>A “re-based” version of Basilisk was released (April 24, 2018), establishing a more stable version of UXP to build upon.
December 17, 2018—>Official release (versioned release) of Basilisk.
2019—>Support for WebExtensions (the newer extension API used by modern browsers) was dropped. The project shifted focus more firmly toward classic (“legacy”) XUL/XPCOM extensions.
2021—>M.C. Straver announced that support for Basilisk would be ended, citing that it had become somewhat redundant to Pale Moon. The browser was also offered for sale.
2022—>A new team (independent of Pale Moon) took over development; Basilisk-Dev became maintainers. The browser remains open source.
Features & What Sets It Apart
Some of the main features and distinguishing characteristics of Basilisk:
Supports XUL / XPCOM (“classic”) extensions which older versions of Firefox and Pale Moon used.
Supports NPAPI plugins — e.g. Java, Flash, Silverlight etc. (though many of these are deprecated/obsolete in modern web usage)
Preserves a Firefox-style interface from versions roughly between Firefox 29 to 56 — sometimes called the “Australis” era UI.
Supports modern web standards where feasible: ECMAScript 6, WebAssembly (WASM), modern cryptography (TLS 1.3 etc.), HTML5, etc.
Does not use newer Mozilla technologies that many current browsers do: no Servo, no Rust components, no e10s (multi-process architecture) in the same way, etc.
Challenges, Criticisms & Changes
Compatibility trade-offs: Because Basilisk keeps many legacy systems, some newer websites/features tied to modern browser tech may not work or may break. WebExtensions support, in particular, was dropped, which limits compatibility with newer add-ons.
Redundancy concern: By 2021, the lead developer considered Basilisk redundant to Pale Moon (which is also using Goanna/UXP) and announced ending official support.
Change of maintainers: In 2022, new independent developers took over to keep Basilisk alive.
Current Status (as of mid-2025)
Basilisk is still being developed (by the Basilisk Browser Development Team, separate from Pale Moon).
It retains its identity as a browser for users who prefer old-style Firefox interface and classic extension/plugin support.
Recent release notes show ongoing bug fixes, security patches, updates to libraries, minor improvements.
The story of Basilisk is not just about a browser; it’s about a fork, a philosophy, and a response to a fundamental technological change in Firefox. It represents a specific branch of Mozilla’s technology dedicated to preserving a legacy platform.
Phase 1: The Predecessor and The Philosophical Split - The Pale Moon Project
To understand Basilisk, you must first understand its parent project, Pale Moon.
Pale Moon’s Origin (2009): Pale Moon began as an optimized fork of Mozilla Firefox, specifically designed for speed and efficiency. Over time, its developers grew critical of the direction Mozilla was taking with Firefox, particularly the move away from the traditional XUL-based interface and the adoption of a rapid-release cycle.
The Fork Becomes Independent: Pale Moon eventually forked its code entirely from Firefox, maintaining and refining the older Goanna rendering engine (a fork of Mozilla’s Gecko) and the XUL (XML User Interface Language) platform. This created a browser that looked and felt like a classic Firefox but was developed on a completely independent path.
Phase 2: The Catalyst - Firefox’s Quantum Leap and XUL Deprecation
Mozilla’s Big Bet (2017): In late 2017, Mozilla released Firefox 57, known as “Firefox Quantum.” This was a massive overhaul that replaced the old Gecko engine with a new, parallelized one (Quantum) and, most critically, dropped support for legacy XUL-based extensions.
The “WebExtensions” API: Mozilla replaced XUL extensions with a new, more restrictive, and cross-browser compatible system called WebExtensions. While more secure and stable, this move broke thousands of powerful, legacy add-ons that many power users relied on.
The Community Divide: This created a major schism in the Firefox community. A significant portion of users and developers felt that Mozilla had betrayed its core power-user base by removing the deep customization that XUL allowed.
Phase 3: The Birth of Basilisk - A Testing Ground and a Statement (2017)
Why Basilisk Was Created: The Pale Moon team, already committed to the XUL platform, created Basilisk for several key reasons:
Platform Development: It serves as a test application for their “Goanna” rendering engine and “UXP” (Unified XUL Platform) before these changes are integrated into the more stable Pale Moon browser. It’s their cutting-edge development playground.
A Viable Alternative: It aims to be a functional, modern(ish) browser that still supports the classic XUL-based extensions Mozilla abandoned.
Ideological Stance: It is a living protest against Mozilla’s shift, demonstrating that a browser based on the older, more powerful XUL/Goanna platform could still be developed and maintained.
What is Basilisk?
Codebase: It is built on the Unified XUL Platform (UXP), which is a community-maintained fork of the Mozilla codebase as it existed before the Quantum switch. It uses the Goanna rendering engine.
Interface: Its user interface is intentionally very similar to Firefox versions 52-56, the last versions before Quantum, to appeal to users who preferred that classic look and feel.
Phase 4: Evolution, Challenges, and Niche Status (2018-Present)
A Development Browser: It’s crucial to understand that Basilisk is explicitly labeled as a “development platform” by its creators. It is less stable than Pale Moon and may have rendering issues or bugs as it tests new engine features.
The Extension Dilemma: While Basilisk supports legacy Firefox extensions (XUL), it does not support the new WebExtensions used by modern Firefox and Chrome. This means its extension ecosystem is frozen in the pre-2017 era, relying on archived add-ons.
Compatibility Challenges: As the web evolves with new standards and APIs, the older Goanna engine in Basilisk (and Pale Moon) can struggle to render some modern, complex websites correctly, especially those heavily reliant on Google’s Blink engine (Chrome, Edge).
Target Audience: Basilisk serves an extremely niche audience:
Pale Moon Testers: Users who want to test the latest UXP/Goanna features.
Die-hard XUL Enthusiasts: Power users who refuse to give up their specific legacy Firefox extensions and customization.
Browser Historians & Ideologues: Those interested in the “what if” path of Mozilla’s technology.
Summary: Legacy and Current Status
Basilisk is not a browser trying to compete for mainstream users. Its history is one of ideological and technological preservation.
A Fork of a Fork: It is a development offshoot of the Pale Moon project, which itself is a fork of the pre-Quantum Firefox code.
The “What If” Browser: It represents what Firefox might have looked like if it had continued to evolve on the XUL/Gecko platform without the Quantum break.
A Niche Development Tool: Its primary purpose is to advance the UXP platform for Pale Moon. Its use as a daily browser is possible but comes with stability and compatibility caveats.
Present Day: The Basilisk project remains in active development, but its progress is tied to the small, dedicated team behind the UXP platform. It stands as a specialized tool for a specific community and a testament to the deep divisions caused by Mozilla’s pivotal decision in 2017.
