Summary of Mozilla products
From MozillaZine Knowledge Base
The Mozilla Suite is Netscape's source code with updates and bugfixes. It has a browser (usually just called 'Mozilla',) a Mail/News reader, an HTML page creation program (Composer,) an Address manager (Address Book,) and an IRC chat client (Chatzilla.)
Firebird is the standalone version of the Mozilla Suite's Browser. Redesigned from scratch to be portable and relativly fast, it is the future replacement for IE. It will be merged into the Mozilla Suite over the next few releases, making for a much faster experience.