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Pale Moon: Technical Details So, you want more details about the browser? I'll be more than happy to explain: Features Supported Processors Differences with Mozilla products How Pale Moon is tested Features/disabled features This browser aims to strike a balance between features and speed/resource use. As such, a choice has been made to consciously disable a few features found in other browsers that are not commonly used by the largest group of users. If you require any of the disabled features, then the main-line build of Pale Moon is not for you! You may find a suitable version on the third party contributed builds page instead. The Pale Moon browser has, among other things, the following features: Optimized for current processors.This browser will not run on museum-grade systems. Increased stability: experience fewer crashes. Support for JPEG-XL, the next-generation image format, as well as the commonly-used web formats (JPEG, PNG, WebP, GIF). We do not support AVIF as it falls technically short in all important areas. Support for Scalable Vector Graphics (SVG) and Canvas drawing. Compatibility with many Legacy Firefox Extensions (add-ons) although we do not provide support for them unless actively supported in our community. Offering low-level API access to extension developers to truly extend browser features. Support for Personas ("lightweight" themes). Support for Complete Themes. CSS Downloadable Font support. Extended HTML5, CSS3 and advanced DOM support. Full and ongoing support for NPAPI plugins (Java, Flash, Silverlight, etc.) Speedy scripting and page rendering. Superior gradients and fonts. Optimized, secure networking. We explicitly try to avoid less secure or questionable networking features like 0-RTT and QUIC. Graphical tab switching with quick-search (user-selectable). More customization options for navigation controls and the tab strip than other modern browsers. Enhanced security indicators (padlock/styling/domain/IDN display). More options for recovery (safe mode/recovery dialog with various repair options). The following features have been disabled or removed by design: Support for specific accessibility hardware. Most people don't have a need for specialized accessibility features for custom input or display devices. This cuts down on the input complexity and internal processing of input and display, but will, obviously, not be suitable for people who need these features. The browser does support more generic accessibility concepts like caret browsing and high-contrast support, and its UI design attempts to follow WCAG guidelines. Parental controls. Pale Moon aims to be a fast browser for general use, not a "secured family browser". The design impact of operating system integrated parental controls as introduced in Mozilla code is significant, and has had serious implications for building the browser. As such, parental controls have been disabled. Extensions-based parental controls are, of course, a just-as viable alternative (and may in many cases work better!). WebRTC. Apart from opening up a whole can of worms security/privacy-wise, "Web Real Time Chat" (comparable with Skype video calls and the likes) is not considered useful or desired functionality for Pale Moon (both according to the developers and the users of the browser at large). This is best left to dedicated programs or at most a browser plug-in. Maintenance service. Pale Moon does not use a Windows maintenance service and does not update silently in the background. Integrated PDF reader. You are always recommended to use a separate, up-to-date document reader for PDF files (as an external program, not as a browser plugin) for your own security, and to have documents displayed in their fully intended format instead of a stripped-down display in an in-browser reader. In-browser DRM. Digital Rights Management using "black box" content-decryption modules to serve a self-imposed DRM-encumbered media market that punishes the wrong parties has no place in Pale Moon. If you wish to use such media, you can use plugins with DRM features like Microsoft Silverlight. Supported processors The Pale Moon browser is specifically optimized for relatively-recent processors and uses instructions exclusively available in more modern processors. This means it will not run on PCs that are particularly old by today's standards, and is likely to display errors or refuse to start on systems with unsupported or poorly supported CPUs. Even if you meet the minimum CPU requirements for the browser, you should not expect wonders from your hardware if it is dated. Modern web browsers are very much alike full-fledged 3D games in the resources and processing power/graphics power they require. Requirements for the regular Pale Moon browser are, in short: a CPU with AVX support. This support has been present in all mainstream CPUs in the last decade. The only exception for official binaries is the 32-bit version we are still building for Windows, which will support much older CPUs. If your CPU does not support the required instruction set, your choice will be to use either a build from source for your specific system, use 32-bit (on Windows), upgrade your CPU to something more modern, or switch to a different browser. While you may also choose to use the last SSE2 version (33.2.1), it is not recommended to do this long-term due to security concerns of using an outdated browser. Our community also provides specific SSE2 builds if none of these options are to your liking, but keep in mind these community builds are not as thoroughly tested as our official distributions. How different is this browser from Mozilla products? While Pale Moon has its ancestral roots in Mozilla Firefox, it should be considered a "true fork" and a totally independent product. Pale Moon is based on a derivative of the Gecko rendering engine (Goanna) and builds on a hard fork of the Mozilla code (mozilla-central) called UXP, a XUL-focused application platform that provides the underpinnings of several XUL applications including Pale Moon. This means that the core rendering functions for Pale Moon differ from Firefox (and other browsers) and websites may display slightly different in this browser. Pale Moon may behave differently when certain advanced configuration preferences are changed. Never assume that what applies to Firefox also applies to Pale Moon; in many cases it does not. Note that "internet speed boosters" and general "tweak guides" written for Firefox can actually harm Pale Moon's speed as the configuration defaults are made with in-depth knowledge of the browser back-end and "a higher number" or "bigger buffer" isn't always better. You are strongly advised to always use defaults as supplied in Pale Moon. Changes were made to the user interface and feature set, to incorporate functionality and visual elements in different locations than what was chosen by the Mozilla team, as well as retaining or re-introducing useful elements that were removed in Firefox, and either removing or disabling (by default) components that would not be used by the average user. In addition, some other user interface changes were made to provide an as consistent and intuitive interface as possible while still staying close to what Firefox's goals have always been. This means the "Australis" or "Photon" interfaces will never be used in Pale Moon. Pale Moon offers more configurability for features, like additional tab preferences, preferences for image loading or tab positions, additional security preferences, and full control over smooth scrolling, to name a few. Pale Moon uses a different "Sync" client and its own server to synchronize data between different instances of the browser. This is not compatible with Firefox Sync as used in Firefox 29 or later. Mozilla's change to "Firefox Accounts" is a different and less secure approach to synchronizing data and focuses more on future commercial endeavours and services of the Mozilla Corporation and, after careful consideration, has been rejected for use in Pale Moon (for quite the list of reasons, to be fair). How Pale Moon has been tested Pale Moon builds are tested for stability before being released by having it used for day-to-day browsing by a number of community members. Of course, specific functional changes are always tested when they are implemented during development. Pale Moon does not rely on CI systems or rigid automated testing methodologies.
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Pale Moon: Technical Details

So, you want more details about the browser? I'll be more than happy to explain:

Features
Supported Processors
Differences with Mozilla products
How Pale Moon is tested

Features/disabled features

This browser aims to strike a balance between features and speed/resource use. As such, a choice has been made to consciously disable a few features found in other browsers that are not commonly used by the largest group of users. If you require any of the disabled features, then the main-line build of Pale Moon is not for you! You may find a suitable version on the third party contributed builds page instead.

The Pale Moon browser has, among other things, the following features:

Optimized for current processors.This browser will not run on museum-grade systems.
Increased stability: experience fewer crashes.
Support for JPEG-XL, the next-generation image format, as well as the commonly-used web formats (JPEG, PNG, WebP, GIF).
We do not support AVIF as it falls technically short in all important areas.
Support for Scalable Vector Graphics (SVG) and Canvas drawing.
Compatibility with many Legacy Firefox Extensions (add-ons) although we do not provide support for them unless actively supported in our community.
Offering low-level API access to extension developers to truly extend browser features.
Support for Personas ("lightweight" themes).
Support for Complete Themes.
CSS Downloadable Font support.
Extended HTML5, CSS3 and advanced DOM support.
Full and ongoing support for NPAPI plugins (Java, Flash, Silverlight, etc.)
Speedy scripting and page rendering.
Superior gradients and fonts.
Optimized, secure networking. We explicitly try to avoid less secure or questionable networking features like 0-RTT and QUIC.
Graphical tab switching with quick-search (user-selectable).
More customization options for navigation controls and the tab strip than other modern browsers.
Enhanced security indicators (padlock/styling/domain/IDN display).
More options for recovery (safe mode/recovery dialog with various repair options).

The following features have been disabled or removed by design:

Support for specific accessibility hardware. Most people don't have a need for specialized accessibility features for custom input or display devices. This cuts down on the input complexity and internal processing of input and display, but will, obviously, not be suitable for people who need these features. The browser does support more generic accessibility concepts like caret browsing and high-contrast support, and its UI design attempts to follow WCAG guidelines.
Parental controls. Pale Moon aims to be a fast browser for general use, not a "secured family browser". The design impact of operating system integrated parental controls as introduced in Mozilla code is significant, and has had serious implications for building the browser. As such, parental controls have been disabled. Extensions-based parental controls are, of course, a just-as viable alternative (and may in many cases work better!).
WebRTC. Apart from opening up a whole can of worms security/privacy-wise, "Web Real Time Chat" (comparable with Skype video calls and the likes) is not considered useful or desired functionality for Pale Moon (both according to the developers and the users of the browser at large). This is best left to dedicated programs or at most a browser plug-in.
Maintenance service. Pale Moon does not use a Windows maintenance service and does not update silently in the background.
Integrated PDF reader. You are always recommended to use a separate, up-to-date document reader for PDF files (as an external program, not as a browser plugin) for your own security, and to have documents displayed in their fully intended format instead of a stripped-down display in an in-browser reader.
In-browser DRM. Digital Rights Management using "black box" content-decryption modules to serve a self-imposed DRM-encumbered media market that punishes the wrong parties has no place in Pale Moon. If you wish to use such media, you can use plugins with DRM features like Microsoft Silverlight.

Supported processors

The Pale Moon browser is specifically optimized for relatively-recent processors and uses instructions exclusively available in more modern processors. This means it will not run on PCs that are particularly old by today's standards, and is likely to display errors or refuse to start on systems with unsupported or poorly supported CPUs. Even if you meet the minimum CPU requirements for the browser, you should not expect wonders from your hardware if it is dated. Modern web browsers are very much alike full-fledged 3D games in the resources and processing power/graphics power they require.
Requirements for the regular Pale Moon browser are, in short: a CPU with AVX support. This support has been present in all mainstream CPUs in the last decade. The only exception for official binaries is the 32-bit version we are still building for Windows, which will support much older CPUs.
If your CPU does not support the required instruction set, your choice will be to use either a build from source for your specific system, use 32-bit (on Windows), upgrade your CPU to something more modern, or switch to a different browser. While you may also choose to use the last SSE2 version (33.2.1), it is not recommended to do this long-term due to security concerns of using an outdated browser. Our community also provides specific SSE2 builds if none of these options are to your liking, but keep in mind these community builds are not as thoroughly tested as our official distributions.

How different is this browser from Mozilla products?

While Pale Moon has its ancestral roots in Mozilla Firefox, it should be considered a "true fork" and a totally independent product.

Pale Moon is based on a derivative of the Gecko rendering engine (Goanna) and builds on a hard fork of the Mozilla code (mozilla-central) called UXP, a XUL-focused application platform that provides the underpinnings of several XUL applications including Pale Moon. This means that the core rendering functions for Pale Moon differ from Firefox (and other browsers) and websites may display slightly different in this browser.
Pale Moon may behave differently when certain advanced configuration preferences are changed. Never assume that what applies to Firefox also applies to Pale Moon; in many cases it does not.
Note that "internet speed boosters" and general "tweak guides" written for Firefox can actually harm Pale Moon's speed as the configuration defaults are made with in-depth knowledge of the browser back-end and "a higher number" or "bigger buffer" isn't always better. You are strongly advised to always use defaults as supplied in Pale Moon.
Changes were made to the user interface and feature set, to incorporate functionality and visual elements in different locations than what was chosen by the Mozilla team, as well as retaining or re-introducing useful elements that were removed in Firefox, and either removing or disabling (by default) components that would not be used by the average user. In addition, some other user interface changes were made to provide an as consistent and intuitive interface as possible while still staying close to what Firefox's goals have always been. This means the "Australis" or "Photon" interfaces will never be used in Pale Moon.
Pale Moon offers more configurability for features, like additional tab preferences, preferences for image loading or tab positions, additional security preferences, and full control over smooth scrolling, to name a few.
Pale Moon uses a different "Sync" client and its own server to synchronize data between different instances of the browser. This is not compatible with Firefox Sync as used in Firefox 29 or later. Mozilla's change to "Firefox Accounts" is a different and less secure approach to synchronizing data and focuses more on future commercial endeavours and services of the Mozilla Corporation and, after careful consideration, has been rejected for use in Pale Moon (for quite the list of reasons, to be fair).

How Pale Moon has been tested

Pale Moon builds are tested for stability before being released by having it used for day-to-day browsing by a number of community members. Of course, specific functional changes are always tested when they are implemented during development. Pale Moon does not rely on CI systems or rigid automated testing methodologies.