Gecko and the NGLayout Engine

Gecko is the code name for the first release of what will become Netscape Communicator 5. Netscape has taken a new approach to building browsers, gone are the days of a new browser version every six months. Partly forced by relentless pressure from Microsoft, Netscape has taken a desperate and possibly brilliant gamble in moving their source code into the public domain. At the same time they have created an independent organization, Mozilla, to oversee developers all over the world who wish to work with the code.


The Open Source model has been very successful for two other pieces of software, the Linux Operating System and the Apache web server. Mozilla completes the picture with client software in the form of the Open Source browser. Mozilla itself only has three full time organizers/managers, the rest of the development is done by people all over the world who contribute their time and energy to create a world class browser based on open standards. In reality, Netscape contributes nearly one hundred developers to the effort and pays their salaries. The hope is the eventually Netscape support will be weaned down and the majority of the work will be handled by out side developers. When Mozilla is done developing this Open Source browser they will release the code to the public and Netscape will use it as the basis for Netscape Communicator 5.0.

Netscape AOL Merger:

The merger of Netscape with AOL has raised a number of questions regarding the future of Mozilla and the development of Gecko and Netscape 5. Even Mozilla has expressed fear over the how they will integrate with AOL. However, Steve Case and AOL have come out and stated that they are very supportive of Mozilla and Open Source effort and plan to continue funding its development. In reality one of the reasons that AOL purchased Netscape is to get access to the NGLayout engine being developed by Mozilla. Because of this AOL is unlikely to kill the goose that lays the golden eggs.

NGLayout Engine (The Heart of Gecko)

So what is the Next Generation Layout Engine (NGLayout) that is so valuable that AOL would turn on Microsoft in order to obtain it? The layout engine is the heart of the browser and makes up the majority of the Gecko . It is the software that takes the standards on the web and translates the code we write to display on screen. It is Layout engine into which the standards are built. The Layout engine also determines how fast pages display on the monitor once they are downloaded. Below is a screen capture of the Gecko browser. As you can see the interface is still similar to Netscape 4, this will change with later releases:

Gecko browser showing embedded tables
The NGLayout is a complete rewrite of the Layout engine used in Netscape 4. Where Netscape 4 was a huge piece of organically developed software with code dating to Netscape 1.0, NGLayout is written to be modular, super quick, and take up little memory. In addition, it is written to support all the latest standards. Being modular the NGLayout engine can be used in other networked devices such as hand held PC Companions such as the Palm Pilot or set top boxes such as WebTV. Expect to see AOL use the NGLayout engine to produce information appliances as part of its AOL Anywhere campaign to make Web and AOL access wireless and ubiquitous.

Until the NGLayout engine is integrated into other products it still is used as the heart of Netscape Communicator. Communicator’s strength has been that it is available on all platforms. Netscape has not given up on this since the complete rewrite of the layout engine. The initial release of Netscape Communicator 5 will most likely include Windows 95, Windows 98, Windows NT 4, Windows NT 5, Linux, Irix and Mac PPC. Other projects are in the works to port to OS/2, Rhapsody, BeOS, Amiga and Windows 3.1.

Standards Support:

The NGLayout engine is built from the ground up with standards in mind, especially the standards from the World Wide Web Consortium (W3C). Netscape has always been very supportive of standards, but it has been argued that Microsoft had better standards support in the Version 4.X browsers. Partly because of the time period in which it came out Internet Explorer has much better support for the Document Object Model (DOM) and Dynamic HTML which results from DOM support. Netscape released Communicator 4.0 before the release of the W3C standard and only included partial support for the DOM and additionally supported the proprietary LAYER tag, which it used for much of its Dynamic HTML.

The final NGLayout is expected to implement a union of the Communicator 4.0 and W3C Level 1 Document Object Models. Full backward compatibility with Netscape 4 is expected. Dynamic HTML compatibility between Internet Explorer and Netscape has been a major issue in the Version 4 browsers. While both companies have vowed to support the DOM, Level 1 from the W3C compatibility is still in question.

Let’s take a look at Gecko’s support and what the final version of the NGLayout engine in Netscape Communicator 5 will support.


Netscape Communicator 5.0

HTML 4.0



Cascading Style Sheets 1



Cascading Style Sheets 2


DOM Level 0 (Equivalent to Netscape 3)


DOM Level 1






As you can see Gecko’s release of the NGLayout engine has very little support for the standards it will eventually support. A sneak preview of sorts is available on Mozilla’s DOM Project page. This page gives the progress on certain projects in the works at Mozilla. From this list it can be seen that the projects to make Netscape Communicator 5 a world class browser for standards support is already underway.


The Gecko browser is a developer’s release, it is not meant to be anything more than a preview of the capabilities to come. In all likelihood it was released to maintain parity with Microsoft who has released a very stable and nearly complete feature set in their Internet Explorer 5.0 beta 2. However, Gecko promises to take the browser far beyond its origins on the computer into embedded systems, net aware information appliances and set top boxes.

Jeff Rule is a principal at RuleWeb Development specializing in DHTML, SMIL, WebTV Interactive TV and Java based multimedia enhancements for advanced media sites. His first book, Dynamic HTML: The HTML Developer’s Guide was published in Decemeber 1998 by Addison Wesley Longman. It features many DHTML multimedia examples from his popular DHTML Demo’s web site.