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Zen Browser vs Mercury: catalog facts
Zen Browser	Mercury
Free Free and open source, funded by donations.	Free Free and open source.
Windows, macOS, Linux	Windows, macOS, Linux
Vertical tabs, workspaces and split view built in, no extensions needed Firefox engine, so Firefox extensions and containers work	Compiler-optimized Firefox builds Privacy patches drawn from LibreWolf, Waterfox and IceCat
Young project; interface changes between releases and bugs surface A small team maintaining a Firefox fork is a real long-term risk	Maintained by a single developer Updates can trail official Firefox releases
Downloadable app	Downloadable app
Open source	Open source
License: MPL-2.0	License: MPL-2.0
No account needed	No account needed
Needs internet	Not stated if it works offline
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked September 23, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.