GNU IceCat is the GNU version of the Firefox browser.

Its main advantage is an ethical one: it is entirely free software.
While the principal source code from the Mozilla project is free
software, the distribution contains various problematic files, the
EULA they require for use of their binaries is troublesome, and they
distribute and recommend non-free software as plug-ins.

In addition, GNU IceCat includes some privacy protection features
included in a separate addon:

1. Some sites refer to zero-size images on other hosts to keep track
   of cookies. When IceCat detects this mechanism it blocks cookies
   from the site hosting the zero-length image file. (It is possible
   to re-enable such a site by removing it from the blocked hosts
   list.)

2. Other sites rewrite the host name in links redirecting the user to
   another site, mainly to "spy" on clicks. When this behavior is
   detected, IceCat shows a message alerting the user.