In August 2005, the GNUzilla project adopted the GNU IceWeasel name for a rebranded distribution of Firefox that made no references to nonfree plugins. By January 1, 2005, rebranding was being referred to as the 'Iceweasel route'. Iceweasel was subsequently used as the example name for a rebranded Firefox in the Mozilla Trademark Policy, and became the most commonly used name for a hypothetical rebranded version of Firefox. It was intended as a parody of 'Firefox'. The first known use of the name in this context is by Nathanael Nerode, in reply to Eric Dorland's suggestion of 'Icerabbit'. During this debate, the name 'Iceweasel' was coined to refer to rebranded versions of Firefox. This policy led to a long debate within the Debian Project in 20.

Unless distributions use the binary files supplied by Mozilla, fall within the stated guidelines, or else have special permission, they must compile the Firefox source with a compile-time option enabled that creates binaries without the official branding of Firefox and related artwork, using either the built-in free artwork, or artwork provided at compile time. The Mozilla Corporation holds the trademark to the Firefox name and denies the use of the name 'Firefox' to unofficial builds that fall outside certain guidelines. In addition, it includes several security and privacy features not found in the mainline Firefox browser. It also maintains a large list of free software plugins. The GNU Project attempts to keep IceCat in synchronization with upstream development of Firefox (long-term support versions) while removing all trademarked artwork and non-free add-ons. Mozilla produces free and open-source software, but the binaries include trademarked artwork. As an internet suite, GNUzilla also includes a mail and newsgroup program, and an HTML composer. IceCat is released as a part of GNUzilla, GNU's rebranding of a code base that used to be the Mozilla Application Suite.

It is compatible with Linux, Windows, Android and macOS. GNU IceCat, formerly known as GNU IceWeasel, is a completely free version of the Mozilla Firefox web browser distributed by the GNU Project. GPL-3.0-or-later (Scripts to convert Firefox into IceCat)

MPL-2.0 (source files from Mozilla Firefox browser)

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