head to head · open source
Zen Browser vs Mercury
Zen Browser has 45,517 GitHub stars, 1,946 forks, 689 open issues and last shipped yesterday. Mercury has 1,542 stars, 43 forks, 92 open issues and last shipped 3 months ago. Zen Browser leads on adoption by 2,852% (45,517 vs 1,542 stars). Zen Browser is written in C++ under MPL-2.0; Mercury is written in JavaScript under MPL-2.0. Zen Browser has attracted 4% as many forks as stars, Mercury 3%. Zen Browser was the more recently maintained of the two, and both are self-hostable with no licence fee. The two share 1 topic tag (firefox), so they are genuine substitutes rather than adjacent tools.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| Zen Browser | Mercury | |
|---|---|---|
| GitHub stars | ★ 46K | ★ 1.5K |
| License | MPL-2.0 | MPL-2.0 |
| Written in | C++ | JavaScript |
| Last push | 2026-11-02 | 2026-08-09 |
| Forks | ⑂ 1.9K | ⑂ 43 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick Zen Browser if
- You weight community size — 46K stars and counting
- You want the MPL-2.0 license terms
- Your stack matches C++
- You value the larger contributor base for long-term maintenance
pick Mercury if
- You want the Mercury feature set and don't need the biggest community
- You prefer the MPL-2.0 license terms
- Your stack matches JavaScript
- You evaluated both and Mercury fits your workflow better
About Zen Browser
Zen Browser Zen is a firefox based browser with the aim of pushing your productivity to a new level! Download • Website • Documentation • Release Notes Firefox Versions Release Is currently built using Firefox version 155.0.1 ! Twilight Is currently built using Firefox version RC 155.0.1 ! Contributing If you'd like to report a bug, please do so on our GitHub Issues page and for feature requests, you can use GitHub Discussions. Zen is an open source project, and we welcome contributions from the community! Please take a look at the contribution guidelines before getting started! Partners Thanks to all the…
read the full Zen Browser overview →
About Mercury
Mercury Browser Firefox fork with compiler optimizations and patches from Librewolf, Waterfox, Ghostery, and BetterFox. It aims to be the Firefox equivalent of my main project: Thorium (a Chromium fork). Patches See PATCHES.md Bugs See BUGS.md Building See BUILDING.md and DEBUGGING.md.
read the full Mercury overview →
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Frequently asked questions
Is Zen Browser or Mercury more popular?
Zen Browser has 45,517 GitHub stars and Mercury has 1,542. Zen Browser has the larger community by that measure.
Are Zen Browser and Mercury free?
Both are open source. Zen Browser is licensed under MPL-2.0 and Mercury under MPL-2.0. Neither carries a licence fee.
What is the difference between Zen Browser and Mercury?
Zen Browser is written in C++ and Mercury in JavaScript. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, Zen Browser or Mercury?
Choose Zen Browser if you want the larger community (45,517 stars) or its MPL-2.0 licence terms. Choose Mercury if its feature set, stack or MPL-2.0 licence fits better. Both are self-hostable.