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).

[5][6] Zen Browser started development on Αpril 1, 2024,[7] after being mentioned in a Reddit post on r/browsers.

The optimized version used Advanced Vector Extensions 2 (AVX2), a CPU instruction set that enhances performance for certain tasks.

[13][14] Zen Browser has many distinct features, like Split View, which allows you to split any number of 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.

Zen Browser has several security features to protect user data and privacy: