Complex sentence: It is called Timberwolf because it's not an official version of Firefox and not part of the main Firefox development repository, and because the name "Mozilla Firefox" is a registered trademark; along with the official Firefox logo.
Split into simpler sentences: It is called Timberwolf because it is not an official version of Firefox and not part of the main Firefox development repository. Also, the name "Mozilla Firefox" is a registered trademark; along with the official Firefox logo.