head to head · open source
Zen Browser vs Mercury
Zen Browser has 44,481 GitHub stars, 1,754 forks, 689 open issues and last shipped yesterday. Mercury has 1,541 stars, 42 forks, 92 open issues and last shipped 1 months ago. Zen Browser leads on adoption by 2,787% (44,481 vs 1,541 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 | ★ 44K | ★ 1.5K |
| License | MPL-2.0 | MPL-2.0 |
| Written in | C++ | JavaScript |
| Last push | 2026-09-17 | 2026-08-09 |
| Forks | ⑂ 1.8K | ⑂ 42 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick Zen Browser if
- You weight community size — 44K 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 is a privacy focused, open source web browser built on Firefox’s Gecko engine. It inherits Firefox’s compatibility and extension ecosystem while introducing a streamlined interface and productivity oriented features. The project lives in the desktop browser ecosystem, targeting users who want a Firefox based experience with reduced clutter and enhanced customization.
read the full Zen Browser overview →
About Mercury
Mercury is a web browser project in the Firefox ecosystem. It is a fork of Firefox that combines compiler optimizations with patches from Librewolf, Waterfox, Ghostery, and BetterFox. The project describes itself as the Firefox equivalent of Thorium, which is a Chromium fork. Mercury is licensed under MPL 2.0, and its repository topics include browser, privacy, optimization, and Firefox fork.
read the full Mercury overview →
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Frequently asked questions
Is Zen Browser or Mercury more popular?
Zen Browser has 44,481 GitHub stars and Mercury has 1,541. 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 (44,481 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.