# Geckium: a Chromium 1 to 58 skin for Firefox 115 and later > Geckium is a CSS and JavaScript modification that makes modern Firefox look and behave like the Chromium releases between 1.0 and 58, brought to you by copying folders into the browser installation, which is both its charm and its risk. **Neo-Kitchenfox/Geckium** — Chrome 1 - 58 theme for Firefox 115+ - Repository: https://github.com/Neo-Kitchenfox/Geckium - Stars: 671 · Forks: 43 - Language: SCSS - License: NOASSERTION - Published: 2026-10-21 · Updated: 2026-10-21 · Language: en - Canonical page: https://hysenlabs.com/projects/neo-kitchenfox-geckium ## What Geckium actually is Geckium is a Mozilla Firefox modification for Firefox 115 and later, written in CSS and JavaScript, that restores the look and feel of past Chromium and Google Chrome releases spanning from 1.0 to 58. The project calls itself a love letter to the history of Chromium and its derivatives, and the artwork at the top of the page shows every era up to Chromium 47 on all three supported platforms. Beyond the visual restoration it brings Chromium Theme support to Firefox, brings obscure prerelease content to the limelight, and retrofits new content into every design. One line is worth repeating because it is the condition for everything else: Geckium is not officially developed, approved or endorsed by Google. It is a community re-creation of another vendor's interface, running inside a browser that has no relationship with that vendor. ## The installation is a file copy, not a package There is no installer, no extension and no package manager entry. The documentation tells you to download Geckium from the releases page, and then to copy two folders from your copy of Geckium into two places in your Firefox installation. The first is your profile, reached by opening Firefox, going to about:support in the address bar, finding Profile Folder next to Open Profile Directory, and copying the chrome folder, plus the chrThemes folder if this is your first installation, into that directory. The second is the browser application itself, and that is where the platform differences bite, because the location of the Firefox application directory is not the same on Linux, Windows and macOS, and the permissions needed to write there differ too. On Linux the target is the firefox or firefox-esr folder under /usr/lib, on Windows you find it from the shortcut's Open file location, and on macOS you go into the application's package contents. Only after the copies do you go back to Firefox, scroll to the top and press Clear startup cache, confirm the prompt, and a Geckium setup window appears. ## The macOS instructions carry a brick warning The macOS section opens with a warning in capital letters that failure to perform the steps properly will brick your current copy of Mozilla Firefox for macOS. The reason is visible in the steps themselves, and it is worth understanding rather than just obeying. On macOS you are told not to quit Firefox, then to find the copy of Mozilla Firefox, right-click it and select Open Package Contents, then go into Contents and then Resources, and copy the Firefox Folder contents there, merging folders if prompted. The instruction not to quit Firefox first is there because a running application holds the package open, and the merge behaviour is left to the file manager because the prompt depends on what is already there. The project links to a wiki page for installing Geckium onto an immutable operating system, which is the same class of problem: a modification that lives inside the application directory does not survive a system that refuses to let you write there. ## The compatibility list is a list of caveats The supported platforms are Linux, tested on Arch, Fedora KDE, Fedora, Kubuntu, Feren OS and Linux Mint, Windows 7, Windows 8.1, Windows 10 with the Native Controls Patch, Windows 11, and macOS, tested on Sonoma and Sequoia. There is a footnote that the macOS 3 to 6 eras may be inaccurate because the maintainers were unsuccessful in finding DMGs of those versions. Then come three limitations that are more informative than the support list. Compatibility with Firefox forks is never guaranteed, with minor adjustments made by Geckium to accommodate itself but issues not seen in Firefox still possible. Ubuntu and the Snap Store are not supported because of how their packages are created, and the project points Ubuntu users at the Mozilla PPA instead. And Flatpak users need to create and install a systemconfig for their browser, if it supports one. In other words, Geckium works where Firefox is a normal installation you can write to. ## The security warning is not boilerplate The instructions include a warning that you should only get JavaScript-powered Firefox modifications from sources you trust, such as the official repository, because JavaScript-powered modifications have full access to Firefox's functionality, including unrestricted access to data inside and outside of Firefox, and file manipulation. That is a fair description of what this project is. Geckium is not a stylesheet, it is code with permission to read your files and talk to the network, installed by copying files into the browser, which means there is no signature, no permission prompt and no sandbox. The project also asks you to install Tampermonkey and, through it, an official Geckium user script for enhanced functionality, which is a second piece of injected code with the same powers. The rule that follows from this is simple: take the download from the project's own releases page, check the file list before copying anything into your browser, and understand that you are granting a community project the ability to run with your browser's full privileges. ## First run restarts Firefox, and that is expected There is a note that once running for the first time, Geckium will restart Firefox automatically one or two times while it sets up required settings, migrations and so on, and that if Firefox does not re-appear after restarting itself, you should terminate Firefox and launch it again, because that is an upstream bug with Firefox. Two things are worth separating here. The restarts are part of the setup rather than a malfunction, since the modification needs to write its own configuration before it can run properly. The failure to re-appear is a separate matter, and the project attributes it to a bug upstream in Firefox rather than to itself. For anyone installing this on a machine they depend on, that combination means the first launch is a moment when the browser may not come back on its own, which is another argument for having a backup of the installation before you start. ## Coming from Silverfox, and what the project says about its own status There is a short section for users of a related modification. If you are coming from Silverfox, the instruction is to install Geckium normally by deleting your chrome folder and placing Geckium's chrome folder in its place, and Geckium will then automatically migrate the settings you had from Silverfox to Geckium's settings. That is a more useful migration story than most, since the two modifications share a structure and the settings live in the same place. The release tags tell you where the project is. The most recent is b0.20.21.2, named Geckium Public Beta 1 Final(?) Community Hotfix, dated 2026-10-08, before it b0.20.20.0 as a Public Beta 1 Community Hotfix from 2026-08-22, and before that b0.20.19.3 with the telling subtitle A final hurrah for pre-relicense, dated 2026-08-01. The last push to the repository was on 2026-10-08, so the project is active, and the tag names suggest a licence change is on the way, with the pre-relicence line closing out. ## Conclusion Geckium fits a Firefox user who genuinely misses the Chrome of 2015 to 2017 and wants the pre-Chromium-59 interface, the old tab strip, the older scrollbars and the general shape of that era, and it fits someone who wants Chromium Theme support in Firefox, which the project also brings across. It does not fit a user who wants a supported browser with a clean update path, because installing it means copying files into the Firefox application directory and the profile, and the project warns that the macOS steps will brick your Firefox if performed wrongly. It also does not fit Ubuntu and Snap users, or Flatpak users without a systemconfig, or anyone on a Firefox fork, since the project states fork compatibility is never guaranteed. Before you install, read the warnings about JavaScript-powered modifications, back up your Firefox installation, and check that the platform you are on is in the tested list. ## FAQ ### What does Geckium do to Firefox? It is a CSS and JavaScript modification for Firefox 115 and later that restores the look and feel of Chromium and Google Chrome releases from 1.0 to 58. It also brings Chromium Theme support to Firefox, brings obscure prerelease content to the limelight and retrofits new content into every design. ### How do I install Geckium? Download it from the releases page, then copy the chrome folder and, on a first install, the chrThemes folder from the Profile Folder in your copy of Geckium into the Firefox profile directory found via about:support, and copy the Firefox Folder contents into the Firefox application directory. Then press Clear startup cache in Firefox and confirm. ### Which platforms does Geckium support? Linux, tested on Arch, Fedora KDE, Fedora, Kubuntu, Feren OS and Linux Mint, Windows 7, 8.1, 10 with the Native Controls Patch and 11, and macOS, tested on Sonoma and Sequoia. Ubuntu and the Snap Store are not supported, and Flatpak needs a systemconfig. ### Is Geckium safe to install? The project warns that JavaScript-powered Firefox modifications have full access to Firefox's functionality, including unrestricted access to data inside and outside Firefox, and file manipulation, and advises getting them only from trusted sources such as the official repository. It also states Geckium is not officially developed, approved or endorsed by Google. ## Sources - [Issues](https://github.com/Neo-Kitchenfox/Geckium/issues) - [Neo-Kitchenfox/Geckium on GitHub](https://github.com/Neo-Kitchenfox/Geckium) - [README](https://github.com/Neo-Kitchenfox/Geckium/blob/main/README.md) - [Releases](https://github.com/Neo-Kitchenfox/Geckium/releases) --- Hysen Labs editorial analysis, written from the project's own repository and release notes. Cite the canonical page: https://hysenlabs.com/projects/neo-kitchenfox-geckium