Intro
What is Mozilla?
Mozilla, in the most concise form, is a web application. To be more precise, it is a suite of applications containing a browser, a mail client, and more. If you are referring to Mozilla as a organization, which is also true, it is an organization that creates the web suite, sub-projects involved with the web suite, a series of products that have spinned off that were created to aid the development of the web suite, spinoffs of the web suite itself, and more.
Mozilla and Netscape
Mozilla and Netscape has had an interesting relationship. Netscape was the company that created Mozilla from Netscape back in its 4.x days. Netscape made Mozilla into an open-source project, with its code being Netscape itself, with a few minor exceptions here and there. An a bunch of people worked on it for quite a while. Finally, the newborn Mozilla organization decided that they would rework the Netscape code into something completely brand new. Fast forward, and you have the release of Mozilla 1.0 and all that commotion. From that point on (actually, a little while before that point), Netscape would be based on Mozilla. Hence, all versions starting from 6.0 are based on Mozilla and everything that is implicated from it. Of course, Netscape added a few things here and there.
The Gecko Rendering Engine
The Gecko rendering engine is the code that decides how all that (X)HTML, CSS, Javascript, etc. should be displayed. Its reputation, which is well deserved, is to be a very modern, standards-support engine, at the loss of support for sites that have long been not well-coded or something along those lines simply because Internet Explorer displays it without a hitch. However, those errors are far and few between and the Gecko rendering engine is usually a blessing for web developers who want to dabble in the latest and the newest in web technologies such as: SVG, XML, XSL, CSS, XHTML, DOM, and other three to four letter acronyms. Beyond that, it works silently in the background to translate code into web pages.
