A look at Firefox forks

Welcome to LWN.net The following subscription-only content has been made available to you by an LWN subscriber. Thousands of subscribers depend on LWN for the best news from the Linux and free software communities. If you enjoy this article, please consider subscribing to LWN. Thank you for visiting LWN.net!

Mozilla's actions have been rubbing many Firefox fans the wrong way as of late, and inspiring them to look for alternatives. There are many choices for users who are looking for a browser that isn't part of the Chrome monoculture but is full-featured and suitable for day-to-day use. For those who are willing to stay in the Firefox "family" there are a number of good options that have taken vastly different approaches. This includes GNU IceCat, Floorp, LibreWolf, and Zen.

How we got here

Mozilla has been disappointing a lot of Firefox users for years, but it seems the pace is accelerating. Its announcement on February 19 that it needs to "diversify" beyond Firefox did not inspire confidence, and it annoyed many who would like to see Mozilla go all-in on its flagship browser (and increase its market share) rather than chasing AI or dabbling in advertising. But a recent and more alarming example is its introduction of terms of use for the browser and the removal of its pledge not to sell users' personal data. Though it has backpedaled somewhat since, and rewritten its terms of use, the damage has been done.

Firefox forking is hardly a new phenomenon. Debian began maintaining forks of Mozilla applications with minimal changes but different names due to conflicts between the Debian Free Software Guidelines and Mozilla's trademark-usage policy. (LWN covered this in 2005.) The era of Iceweasel, Debian's brand name for Firefox, came to an end in 2016. Note that the name Iceweasel is not merely a play on the name "Firefox"; its origin is one of Matt Groening's Life in Hell comic strips (here), which contained a fictional quote attributed to Friedrich Nietzsche.

Love is a snowmobile racing across the tundra and then suddenly it flips over, pinning you underneath. At night, the ice weasels come.

The GNU project also adopted the name IceWeasel for the GNUzilla project—basically Mozilla source code with any non-free code, such as the Adobe Flash Player, stripped out. In 2007, Karl Berry announced that GNUzilla would be adopting the name IceCat for its version "not because we have anything against weasels" but to avoid confusion with Debian's version.

GNU IceCat

IceCat has the distinction of being the oldest Firefox fork still in development. Ray Dryden applied for GNUzilla to become part of the GNU Project in August 2005, and test releases based on Firefox 1.5.0 were available later that year. IceCat, as with all of the forks covered in this article, is available under the Mozilla Public License (MPL) 2.0. However, the scripts and other tools used to create an IceCat release from Firefox are licensed under the GPLv3.

GNUzilla does not distribute binaries of IceCat. The project recommends using GNU Guix to install IceCat on x86_64 Linux systems, and also makes its scripts available in its Git repository to compile IceCat from Firefox's extended-support releases (ESRs). It may, however, also be packaged for a user's favorite Linux distribution. Fedora 41, for example, currently has IceCat 115.20.0esr—which is based on Firefox 115.20.0; both were released on February 4.

Current-day IceCat has several changes that distinguish it from Firefox. The most immediately obvious is its use of the LibreJS add-on to block "nonfree nontrivial JavaScript while allowing JavaScript that is free and/or trivial". In practice, this means that a significant number of sites will not work unless the user adds exceptions for the JavaScript used by the site. Users can choose to add exceptions for individual scripts blocked by LibreJS or to add an exception for the entire site. Even LWN, which uses a minimal amount of JavaScript, has scripts that are blocked by LibreJS.

IceCat includes the JShelter extension, which attempts to block not just malware, but browser fingerprinting and user tracking as well. It modifies the JavaScript environment that is available to web pages to try to confuse fingerprinters and make it more difficult to carry out attacks using JavaScript. It may block APIs or return fake values to thwart these attempts. Like LibreJS, it can be modified or turned off entirely for specific sites. There is a paper from 2022 that explains the extension's approach in great detail, and an extensive FAQ that may be of use in troubleshooting interactions between JShelter and web sites.

In a similar vein, IceCat includes a fork of the Third-party Request Blocker extension that (as the name implies) blocks connections to third-party resources without user consent. It is a little concerning that the page describing the extension describes it as "seemingly maintained by 'sw'", and its last update was in March 2020. The home page listed for the extension is no longer available. Despite the lag in development, it still seems to be working and blocking plenty of third-party requests. A visit to a site like The Guardian, for instance, shows seven sites blocked. As the screenshot shows, site layout and images are often affected by IceCat's default settings. Usually the sites are still usable, but far less aesthetically pleasing.

One thing that worked well for me was to enable just enough to see the page text and then use the reader view to read a site's articles or other content. (Sadly, none of the forks offer a "browse everything in reader view by default" option.)

In all, IceCat ships with eight extensions that either attempt to enhance user privacy, block non-free software, or unbreak sites that are affected by its other extensions. It includes a "LibreJS/USPS compatibility" plugin to offer an alternative shipping calculator for the US Postal Service site as well as an extension to replace JavaScript blocked by LibreJS on the Library Genesis sites.

The project has an extension-finder service called Mozzarella, which (of course) only lists extensions that are free software. However, the extensions may be outdated compared to their counterparts listed in Firefox's add-on catalog. For example, the Privacy Badger extension in the Mozzarella catalog was last updated in June 2023. The Firefox catalog version was last updated on January 29, 2025.

Right now, three people are listed as maintainers for GNUzilla: Ruben Rodriguez, Amin Bandali, and Mark H. Weaver. The development mailing lists are a bit on the quiet side. The last-archived conversation currently for the gnuzilla-dev list is from August 2024. The bug-gnuzilla list is a little more lively—its last activity was in December 2024.

IceCat is probably a good choice for folks who are more concerned with the free software ethos and privacy than with functionality.

Floorp

The Floorp project is a much newer entrant. It is developed by a community of Japanese students called Ablaze. Development is hosted on GitHub, and the project solicits donations via GitHub donations. According to its donations page, donors who contribute at the $100 level may submit ads to feature in the new tab page—but the ads, which are displayed as shortcuts with a "sponsored" label, can be turned off in the settings. I've been unable to find any information about the project governance or legal structure of Ablaze.

Its contributors page lists seven primary maintainers and 39 code contributors, as well as many people who have contributed to its language packs and translations, or who maintain packages. Floorp does not offer native packages for Linux distributions, but it does provide a Flatpak via Flathub and precompiled releases for x86_64 and ARM64.

Originally Floorp was based on Chromium but switched to Firefox in early 2022. The first Firefox-derived version was Floorp v7 (announcement in Japanese), and it was based on the Firefox rapid releases, but the project switched to the ESR releases as their base with v8. The most recent release, version 11.23.1, was announced on February 15, and is based on (according to about:config) the Firefox ESR 128.8.0 release, which came out on March 4. It would be nice if the project were more explicit in its release notes about which version of Firefox a release was based on. This is not merely for curiosity's sake—it would help users track whether Floorp was receiving the most recent security updates. The project has said that it plans to move back to the rapid release versions of Firefox with v12, which is currently in beta.

The project promises "strong tracking protection" and that it does not track users or have any affiliation with advertising companies. However, the project does not give details on how its tracking protection differs from Firefox's. It still uses Google as its default search engine and includes the Firefox browser sync feature. It also uses Mozilla's add-ons repository, and should work with most Firefox add-ons that are compatible with the corresponding Firefox version.

Floorp does have a number of interesting features and enhancements that may tempt users. It has a dual-sidebar layout that allows users to access bookmarks, history, and other tools on the left-hand side, while the right-hand has the Web Apps panel. Users can add web sites to open in the Web Apps panel, which can be useful while (for example) doing research for an article while keeping a version of the article open in the panel.

In addition to the Apps panel, Floorp has a split-view feature that lets users open two pages side-by-side by selecting a tab and clicking "Split this Tab". Each split has its own history and URL bar. Floorp's layout is great for wide-screen monitors, and I like the ability to open sites in split view rather than juggling multiple browser windows.

Another interesting inclusion in Floorp is its Workspace feature. This allows users to group tabs by categories like "work", "comics", "shopping", or whatever makes sense for the users' browsing habits. I've found this useful for working on projects and stories for LWN—I might have a dozen tabs open for a specific story, which I can group into a single workspace. Workspaces can also be assigned to Firefox's multi-account containers. For example, a user might want to log in to the same site using different accounts—without having to sign in and out repeatedly. Combining the workspace and multi-account containers can be useful in a number of scenarios.

Firefox's tabs have seen little feature advancement in the past few years. Floorp adds a few much-needed enhancements here, allowing users to move the tab bar to the bottom of the window, use a multi-row tab bar, and even a vertical tab bar. However, the Floorp implementation of the vertical tab bar will go away in v12, now that Mozilla has finally added vertical tabs in Firefox 136.0.

Overall, Floorp is an interesting project with some nice enhancements to the Firefox UI. However, the development roadmap seems a bit more haphazard than I would like—switching back and forth between Firefox rapid release and ESRs, for example. That may not dissuade other folks, though.

LibreWolf

The LibreWolf project got its start in 2020. Its focus is primarily around privacy, security, and the removal of "anti-freedom" features, such as telemetry and DRM, from Firefox. It lists seven core contributors on its home page and points to its Matrix room for development discussions. Its development is hosted on Codeberg.

LibreWolf is available in the Arch User Repository (AUR) for Arch Linux users; and the project offers its own package repositories for Debian-based distributions and for Fedora. It recommends its Flatpak packages for most other distributions. The most recent version of LibreWolf is 135.0.1, which was a minor update based on Firefox 135. The first LibreWolf 135.0 release came out on February 9, about five days after the upstream Firefox version.

LibreWolf has the normal configuration options one would expect for a Firefox fork, but it also has the option of using a special configuration file called librewolf.overrides.cfg to set preferences that can take effect across multiple profiles rather than having to tweak the configuration for each profile. It also makes preferences easy to back up and move to a new machine. The documentation explains where to find this file, depending on the installation method, and offers several suggestions for possible preference changes.

LibreWolf is mostly notable for what it doesn't have rather than what it does. That is, it removes other features from Firefox that have not been well-received many users such as Pocket integration, telemetry, and more. Firefox Sync is disabled by default but it can be enabled in settings.

LibreWolf does include the uBlock Origin add-blocker add-on as part of its standard installation. It should be noted that uBlock Origin is being disabled for Chrome users as Google phases out support for the WebExtension API V2 in favor of V3, which will curtail features that uBlock Origin and other add-ons require to function. To its credit, Mozilla has committed to continuing its support for Manifest V2 and V3. LWN covered Manifest V3 and its impact on content blockers in 2021.

For the most part, users would be hard-pressed to spot many differences between LibreWolf and Firefox at first (or second) glance, so a screen shot of LibreWolf seemed a bit unnecessary. That approach is likely to appeal to many users who are uneasy with things like telemetry and Pocket, but don't want an entirely new browsing experience.

Zen

The Zen browser project is the most recent entrant. Its development began last year with an announcement on Reddit. It is currently in beta, with its most recent version, 1.8.2b based on Firefox 135.0.1, released on February 25. Kudos to the Zen project, by the way, for proudly including the Firefox version alongside the project version in its "About" dialog—information that literally every other Firefox fork seems intent on hiding. Zen lists 12 people in the main project team, and about 90 contributors to the browser. Development for Zen is hosted on GitHub, and discussion takes place on Discord (link goes to a Discord invitation).

Like Floorp, the project solicits donations to assist with development, but little information seems to be available about its governance or structure to provide transparency about how the money is spent.

Unlike the other forks, it is not immediately obvious that Zen is an offshoot of Firefox. It does not look at all like the standard Firefox interface, even before users start customizing it. Even Floorp, which allows significant customization, still bears some resemblance to Firefox on first use. Zen sports a tab sidebar on the left that blends the Workspace concept from Floorp and vertical tabs, with a set of default bookmarks ("Essentials") as icons at the top. The browser menu is located in the top-left corner, indicated by a button with three dots. The window title bar is hidden and only appears if a user hovers the mouse at the top of the window for a few seconds.

While Zen looks modern and interesting, its sleek user interface and configurability comes at the cost of intuitive usability in some cases. For example, one might expect that setting Zen to light mode in the "Language and Appearance" settings would also change the browser's interface to light mode. It does not, as shown in the screenshot. Instead, a user has to go to the "Add-ons and Themes" settings to select a light theme. It would help a great deal if Zen's user guide were more complete, but it only has a little bit of documentation to offer at the moment. To be fair, it is still a beta project, so it may be much improved by the time the Zen browser has its first stable release. For now, users will need to be ready to dig through Reddit and other forums for tips.

Features like glance, which pre-fetches a link and gives a preview of it before opening it in a new tab or window, are useful, but not at all obvious how to use, even if one is aware the feature exists. (On Linux, activate glance with Alt+click.) Likewise, Zen's split-screen mode requires the user to select multiple tabs and then right-click to select "Split Tab". Rearranging the splits is also not intuitive. That said, the additional features are compelling if one is willing to do some searching to figure things out.

The Zen interface can be customized extensively to suit individual tastes via the settings. If those options aren't enough, Zen has its own set of add-ons and extensions called Mods to modify the interface or add features. This ranges from a green-hued theme called Matcha to tweaks to further minimize the sidebar. Most Firefox add-ons should work with Zen as well, though some may clash with its user-interface changes.

Currently, Zen isn't fully baked enough for me to consider switching to it. Others may be more adventurous in their browsing habits than I am, though. I can say that it has stabilized significantly since I first tried it shortly after its first public release. The project does bear keeping an eye on, and the Mozilla folks could do worse than to copy some of the ideas (and code) that the project is experimenting with.

Others

The Firefox fork rabbit hole is surprisingly deep. There are a few alternatives I chose not to try—but mention here for completeness—and probably a few that I've missed. The Basilisk project is a kind of retro-Firefox project that aims to retain technologies that Firefox has removed. This includes the deprecated Netscape Plugin Application Programming Interface (NPAPI) plugin support, ALSA support on Linux, XUL extensions, and more.

Waterfox is a browser that began in 2011 as an independent project by Alex Kontos while he was a student. It was acquired and then un-acquired by Internet-advertising company System1. Its site does not, at least at the moment, have enough specifics about the browser's differences and features to compel me to take it for a test drive.

The Pale Moon project is another browser that has forked off of Mozilla Firefox code and no longer tracks it directly. It uses the Goanna fork of the Gecko rendering engine and still supports NPAPI plugins and XUL extensions. The project promises no telemetry or data gathering. It offers a somewhat nostalgic look and feel that is similar to Firefox in the mid-2000s.

For those who pine for the days of the Netscape suite that included the browser, mail client, HTML editor, IRC chat, and more, there is SeaMonkey. The project uses code from Firefox and Thunderbird, though it is not directly based on recent versions. According to its site, it backports security fixes from Firefox and Thunderbird ESRs that apply to SeaMonkey. The project also maintains the Composer HTML editor and ChatZilla IRC client that are no longer maintained by Mozilla. SeaMonkey is still packaged for a number of Linux distributions, and binaries are available for Linux on x86_64 and x86 as a tarball. It might be a good option for users who are still using 32-bit x86 Linux systems.

Still dependent on Mozilla

Regardless which Firefox fork one chooses, it is important to remember the downsides. First and foremost, all of the forks are dependent on Mozilla to do the heavy lifting. The bulk of development is carried by Mozilla, the direction of Firefox is set by Mozilla, and choosing to run a fork puts the user one step removed from security and bug fixes. This does not mean users shouldn't consider one of these forks, but they should be aware of the potential downsides.

There is some precedent for soft forks displacing the original upstream. For example, the Go-oo fork of OpenOffice.org became LibreOffice after Oracle consumed Sun.That fork has clearly overtaken OpenOffice.org in the Linux community as the go-to desktop office suite and its development has eclipsed that of its counterpart Apache OpenOffice. Go-oo, of course, had corporate support as well as community support. For a Firefox fork to be truly independent and sustainable, it would need a similar effort behind it. Thus far, no such movement has materialized.

A recent question on the LibreWolf issue tracker drives that point home nicely. User "kallisti5" asked if LibreWolf was prepared to fork Firefox "if Mozilla continues farther down this path?" One of LibreWolf's contributors, "ohfp", replied that the project was "absolutely not prepared to do that" due to limited time and energy to work on the project as it is. "We would not even remotely be able to fork and maintain a browser fully, let alone to continually develop and improve it."

Another downside to the forks is that there are far fewer eyes on their code and communities. When Mozilla makes an important move, whether it's positive or negative, users are likely to hear about it quickly. As of now, the forks get relatively little attention.

Folks who want to jump ship from Mozilla's ecosystem entirely, while still sticking to open source, have some options. Ladybird, which LWN covered in June last year, is an attempt to create a new browser from whole cloth. It is an interesting effort, but not ready for day-to-day use for most folks. Qutebrowser, Nyxt, and NetSurf are also worth a look—though they may have some drawbacks for day-to-day use in terms of site compatibility and features. We will take a look at some of those options soon.