GNUzilla is the GNU version of the Mozilla suite, and GNU IceCat is
the GNU version of the Firefox browser. Its main advantage is an
ethical one: it is entirely free software. While the Firefox source
code from the Mozilla project is free software, they distribute and
recommend non-free software as plug-ins and addons. Also their
trademark license restricts distribution in several ways incompatible
with freedom 0. Icecat includes the following privacy protection
features:

LibreJS: GNU LibreJS aims to address the JavaScript problem described
in Richard Stallman's article The JavaScript Trap.

Https-Everywhere: Extension that encrypts your communications with
many major websites, making your browsing more secure.

SpyBlock: Blocks privacy trackers while in normal browsing mode, and
all third party requests when in private browsing mode. Based on
Adblock Plus.

AboutIceCat: Adds a custom "about:icecat" homepage with links to
information about the free software and privacy features in IceCat,
and checkboxes to enable and disable the ones more prone to break
websites.

Fingerprinting countermeasures: Fingerprinting is a series of
techniques allowing to uniquely identify a browser based on specific
characterisics of that particular instance (like what fonts are
available in that machine). Unlike cookies the user cannot opt-out of
being tracked this way, so the browser has to avoid giving away that
kind of hints.