GNU IceCat, formerly known as GNU IceWeasel, is a free web browser distributed by the GNU Project. It is based on the Mozilla platform and is available for installation on GNU/Linux, Windows, macOS and Android.
IceCat includes additional security features such as the option to block third party zero-length image files resulting in third party cookies, also known as web bugs. The software also provides warnings for URL redirection and has functionality to set a different user agent string for different domains.
The name “IceCat” was coined to show our relationship to the Mozilla Firefox browser. Ice isn't Fire and a Cat isn't a Fox, so it is clearly a different package (we don't want Mozilla blamed for our mistakes, nor cause confusion with their trademarks), but is equally clearly intimately related (of course nearly all of the work comes from the Mozilla foundation effort, so we want to give credit). Previously, this GNU browser project was also named IceWeasel, but that proved confusing.