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HellFire vs Mercury: catalog facts
HellFire	Mercury
Free Free to download from the GitHub releases page.	Free Free and open source.
Linux	Windows, macOS, Linux
Unmodified Firefox behaviour and appearance with compile-time optimizations Build configuration and patcher script are published in the repository	Compiler-optimized Firefox builds Privacy patches drawn from LibreWolf, Waterfox and IceCat
Builds only for x86_64 Linux; Windows support was dropped License is not clearly stated in the repository metadata	Maintained by a single developer Updates can trail official Firefox releases
Downloadable app	Downloadable app
Closed source	Open source
License not stated	License: MPL-2.0
No account needed	No account needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked September 23, 2026

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