The following outline each of browsers and what role they play in web development.

Microsoft Internet Explorer

Internet Explorer is Microsoft’s browser that comes preloaded with the Windows operating system. The current version, as of this writing, is version 6. Microsoft discontinued development of the Internet Explorer browser as a standalone application for Windows and announced that Internet Explorer will no longer be developed for other operating systems.

That translates into no more Internet Explorer for the Macintosh. Instead, Microsoft plans for Internet Explorer to be completely integrated with its next operating system, codenamed Longhorn. Internet Explorer will no longer be its own application but a smaller part of the larger operating system.

Consequently, updates to Internet Explorer will only be available with operating system updates and upgrades. In the meantime, updates to the current Internet Explorer 6 browser will come in the form of service packs and updates to the Windows XP and Windows 2000 operating systems via the Windows Update mechanism provided with Windows.

According to Microsoft, this will not include updates to Internet Explorer’s CSS capabilities or increased support for other web standards. What does this mean for users and developers? Internet Explorer 6, released in 2001, is the last version of Internet Explorer until the release of the next Windows OS, Longhorn, currently projected for 2006.

That leaves a gap of several years before developers will have access to improved support for CSS and other web standards in Microsoft’s flagship browser. At the time of this writing, Internet Explorer is already aging rapidly.

This means developers are likely to be stuck developing for Internet Explorer 6 for a good few years, coding around features that it does not support and dealing with bugs in the features that it does support.

Internet Explorer’s global market share has also been on the decline. At the time of this writing, this decline in market share is mostly among technically inclined people. People in the information technology industry have been switching more and more to Mozilla, an open-source browser with far more advanced support for web standards.

Current statistics indicate that some websites receive as many as 20% of visitors using a Mozilla browser, although this figure can be much higher or lower depending on the website and its target audience. This figure should not to be taken lightly, however, as the number has been steadily rising over the course of 2004.

Despite the decline in its use for some websites, Internet Explorer is still the dominant browser, garnering from 70% to 90% of the browser market share for most websites.

Gecko: Mozilla, Mozilla Firefox, and Netscape

Gecko was created in January 1998. At that time, Netscape announced that it was making its browser free to its users and that its browser would be open source, meaning that its source code would be freely available for modification and distribution. This led to the creation of Mozilla, the organization that develops and manages the Netscape code.

America Online later purchased Netscape, and until July 2003, Mozilla remained a part of Netscape. In July 2003, the Mozilla Foundation was created, making Mozilla an independent, not-for-profit corporation.

When the Netscape browser became open source, its rendering engine, the part of the browser software responsible for making the source code of a web page into something you can see and interact with, was given the name Gecko.

Gecko is the foundation that a whole suite of browsers relies on to do the behind-the-scenes work of rendering web pages. Gecko is included in AOL for OS X, Netscape 6, Netscape 7, Mozilla, and Mozilla Firefox browsers.

Netscape’s browser market share has greatly diminished, whereas Mozilla continues to gain in popularity, occupying the number-two spot by most statistical estimates. The following table charts the relationship between Mozilla and Netscape browsers; the version relationships here show the corresponding version of Gecko shared between the two browsers.

For instance, Netscape 7.2, which is the latest Netscape browser at the time of this writing, is based on the Gecko software inside Mozilla 1.7; and the two can be expected to behave the same as far as CSS is concerned.

The Mozilla browser is more than just a browser. It includes an e-mail client, an Internet Relay Chat (IRC) client, and a web page-authoring tool. However, this extra functionality doesn’t appeal to everyone who uses a web browser. In fact, an average web user is unlikely to use anything but the browser itself.

All this extra functionality also significantly increases the size of a Mozilla download. This, and other considerations, led the Mozilla foundation to create yet another browser. An application that includes only the browser was initially released under the name Phoenix, a name symbolic of a browser rising from the ashes of the overly complicated Mozilla browser and its Netscape predecessor.

It was later renamed Firebird because of threats of trademark infringement from a company already using the Phoenix name; still later, the name was changed to Firefox to avoid conflicts with another open source project named Firebird.

Now, settled on the name Firefox, Mozilla Firefox also uses the Gecko rendering engine to present web pages; it can be thought of as the browser part of the Mozilla browser.

Opera

Opera is a lesser-known, Norwegian-based company. Opera users are fewer, accounting for only a few percent market share by most statistical estimates. Again, that figure can be much higher or lower depending on a website’s audience.

Also be aware that Opera and Mozilla Firefox browsers can be configured to identify themselves to a website as Microsoft Internet Explorer browsers. This, of course, can distort statistical analysis.

This spoofing is done because websites often create content targeting Microsoft Internet Explorer and Netscape specifically, leaving everyone else out in the cold—even though third-party browsers like Mozilla Firefox and Opera probably support the required functionality.

At the time of this writing, the current version of the Opera browser is 7.54. You can download this browser for free from www.opera.com. The free version of Opera includes a window that displays advertisements. The Opera browser is available for Windows, Macintosh, Linux, and a variety of other platforms.

KHTML: Safari and Konqueror

The last browser that I discuss is Safari, which is based on Konqueror, itself an open-source browser available for Linux operating systems. The rendering engine used in the Safari and Konqueror web browsers is called KHTML.

Safari is developed by Apple and is the browser included with Macintosh OS X operating systems. Previous to Safari, Internet Explorer and Gecko had been dominant on the Mac. Safari behaves in much the same way as Gecko.