Actually it is the other way around. The netscape 6.x series is based on the Mozilla code. Mozilla is based on netscape's gecko rendering engine. However, the codebase IS NOT identical between netscape 6.x and Mozilla.
You can change the appearance of the browser. Look under View/Apply Theme. There are only 2 installed by default classic and modern. There are many themes you can download View/Apply themes/Get new themes.