# Zen Browser

Zen Browser is a free and open-source fork of Mozilla Firefox, with its main focus being privacy, customizability and design, and it is licensed under the Mozilla Public License 2.0 (MPL 2.0).

## Development

Zen Browser started development on April 1, 2024, after being mentioned in a Reddit post on r/browsers. On July 12, 2024, the first public release of Zen Browser was released as an Alpha build, named 1.0.0-a.1. As of December 2024, there are a total of 104 contributors to Zen Browser, 52 desktop contributors and 52 site contributors. Zen Browser also has a Twilight build, an unstable experimental build for testing the latest features. On December 10, 2024, Zen entered its beta phase, and launched its new "Zen" branding, featuring a new logo and a new website, with its new tagline: "Welcome to a calmer internet".

## Compatibility

Zen Browser is compatible with Microsoft Windows, macOS and Linux. It had three download options: optimized, made for newer systems; generic, made for older systems; and ARM64, made for devices that run on ARM64 architectures. The optimized version used Advanced Vector Extensions 2 (AVX2), a CPU instruction set that enhances performance for certain tasks. This instruction set is available only on modern processors. The optimized builds were discontinued in December 2024 due to high power consumption, user confusion, and incompatibility with other Clang optimizations.
The Linux version is available for download as a Flatpak, AppImage and as a Tarball. The macOS and Windows version are available for x86_64 and ARM64.

## Features

Zen Browser adopts the vertical tabs philosophy, which has been observed in other browsers like Vivaldi, Microsoft Edge and Brave, and is especially prominent in Arc Browser. Similar to Arc, vertical tabs are central to Zen's identity, but there are plans to implement horizontal tabs like a traditional browser in a future release.
Zen Browser has many distinct features, like Split View, which split websites into multiple tiled panes inside a single window; Zen Sidebar, a built-in detachable sidebar for quickly opening websites side-by-side; and Zen Glance, a feature to quickly preview a website without leaving your current page, and workspaces that let you separate your tabs.

## Reception

Liam Proven from The Register praised Zen Browser for being a "Google-free browser".
Jack Wallen of ZDNet praised Zen for being the "customizable Firefox".

## Zen Mods

Zen Mods (formerly called Themes Store) is a Zen Browser feature which uses custom-made UGC themes which can only be compatible with Zen. As of March 16th, 2025, the Zen Mods page has 87 total themes, further adding to the customizability of the browser.

## Security

Zen Browser has several security features to protect user data and privacy:
* Built on latest Firefox version: Zen Browser is based on the most recent version of Firefox, benefiting from Firefox's security updates and patches.
* Tracking protection: The browser includes tracking protection, blocking third parties from tracking users' online activities.
* OCSP support: Zen Browser uses the Online Certificate Status Protocol (OCSP) to verify the validity of websites' SSL certificates, enhancing security against expired or revoked certificates.
* Strict SSL standards: Insecure SSL connections are treated as broken by default, and Zen Browser blocks connections to websites that do not meet modern security standards.