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Mercury vs HellFire: catalog facts
Mercury	HellFire
Free Free and open source.	Free Free to download from the GitHub releases page.
Windows, macOS, Linux	Linux
Compiler-optimized Firefox builds Privacy patches drawn from LibreWolf, Waterfox and IceCat	Unmodified Firefox behaviour and appearance with compile-time optimizations Build configuration and patcher script are published in the repository
Maintained by a single developer Updates can trail official Firefox releases	Builds only for x86_64 Linux; Windows support was dropped License is not clearly stated in the repository metadata
Downloadable app	Downloadable app
Open source	Closed source
License: MPL-2.0	License not stated
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 September 23, 2026	Official website Full listing and sources Checked October 2, 2026

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