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

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