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: