GNU IceCat is a free and open-source web browser from the GNU Project. It is a fork of Mozilla Firefox, modified to ensure it contains 100% free software and to enhance user privacy.
Iceweasel was not a separate web browser; it was simply a renamed version of Mozilla Firefox.
CometBird was a short-lived, niche web browser that was essentially a lightly modified version of Mozilla Firefox
LibreWolf is a privacy-focused, open-source web browser designed to be a secure and private version of Firefox.
TenFourFox was a specialized web browser designed to run on older, PowerPC-based Apple Macintosh computers
Swiftfox was a optimized version of Mozilla Firefox specifically for Linux, designed for one purpose: raw speed.
FireDragon is a performance-optimized, privacy-hardened web browser for Linux, specifically designed for the Garuda Linux distribution.
Firefox Focus is a streamlined, privacy-focused mobile browser designed for automatic, single-session browsing
Catalyst is a niche, independent web browser for Windows, developed by a single programmer, César Claudio Lóriga González. It has been in active development since around 2016.
The project was eventually abandoned, its website shut down, and it is now considered obsolete and unsafe to use. It is remembered as a charming but unsuccessful experiment in browser design.
Blue Hawk is a highly specialized, niche web browser focused on maximum security, now considered obsolete and unsafe
Polypane is a specialized, premium web browser built specifically for web developers and designers