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.
[^] # Re: Laisse la FSF le faire
Posté par psychoslave__ (site web personnel) . En réponse au journal Ça vous dit de forker Chromium?. Évalué à 2.
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.
source : http://www.gnu.org/software/gnuzilla/