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.
emphasized by me
I want to understand the trademark license restriction. And how Firefox is not completely free. I would also like to ask: What are the differences between Firefox and IceCat?