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Introducing Basilisk, an open source XUL based browser and “close twin” to pre-Servo Firefox

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  • 2 min read
  • 18 Dec 2018

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Yesterday, the team behind Pale Moon, an open-source web browser introduced Basilisk, which is supposedly a “close twin to Mozilla's Firefox”. Basilisk is an open source web browser which is based on Mozilla’s XML User Interface Language (XUL). It is being introduced as primarily a reference application for development of the XUL platform it builds upon. It features Firefox-style interface and operation.

What are the features of Basilisk?

  • It uses Goanna as layout and rendering engine, which is forked off of the Firefox’s browser engine called Gecko.
  • Builds on UXP, a XUL platform in development.
  • As it does not uses Rust or Photon user interface, users can expect the user interface to be similar to Firefox between v29 and v56.
  • It does not use Electrolysis or e10s, which aims to bring multi-process architecture to Firefox. It splits the Firefox browser into a single process for the UI, and several processes for web content, media playback, plugins, etc.
  • It does not require walled-garden extension signing.
  • To provide users a modern web browsing experience it supports the ECMAScript 6 standard of JavaScript.
  • Supports all NPAPI plugins such as Unity, Silverlight, Flash, Java, authentication plugins, etc.
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  • Supports XUL/Overlay Mozilla-style extensions.
  • Comes with experimental support for WebExtension.
  • Supports ALSA on Linux
  • Supports WebAssembly
  • Supports advanced Graphite font shaping features
  • Supports modern web cryptography such TLS 1.3, modern ciphers, HSTS, etc.


Basilisk is still in its development phase or in beta, which means that it may have some bugs and is provided as-is, with potential defects.

Many developers are confused about how Basilisk differs from the Pale Moon browser the team offers and also why anyone would want to use pre-Servo Firefox. While some users say, “My interpretation is that this is mostly a project for the die-hard users who lost support for niche extensions they really liked when XUL left mainstream Firefox... it reads mostly like they intend to maintain it as a time capsule. "No different from last time" is exactly the main selling feature.

To read more in detail, visit Basilisk’s official website.

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