Although Microsoft still dominates the web browser space, its Internet Explorer continues to lose market share to open-source rival Mozilla.
Internet Explorer held more than 95% of the US browser market for several years, but its share dropped to 94.7% in July and had declined further to 92.9% on 29 October, WebSideStory, a web metrics company, said.
Benefiting from high-profile security vulnerabilities in the Microsoft browser and recommendations by experts to switch, the Mozilla Foundation saw its market share rise.
The Mozilla Suite, Netscape and Firefox held 6% of the market at the end of October, up from 3.5% in June, said WebSideStory.
"It is not a fast drop for Internet Explorer, but it might be considered a fast gain for Mozilla," said Geoff Johnston, an analyst at WebSideStory.
Firefox is the Mozilla Foundation's standalone browser. The Mozilla Suite includes a browser, e-mail client, internet relay chat client and web page editor.
Netscape, distributed by America Online (AOL), is based on Mozilla technology. The Mozilla open-source project was started in early 1998 by Netscape.
The rise of Firefox has been especially remarkable, Johnston said. The browser - a 1.0 version of which is scheduled to be released 9 November - held 3% market share at the end of October.
Firefox was introduced in February this year when Mozilla renamed its Firebird project.
"It was one thing in July to see Microsoft starting to lose market share for the first time in a trend-like fashion. But we did not know whether it would continue. It has," Johnston said.
Taking advantage of the momentum, the Mozilla Foundation is drumming up support for Firefox. The group has collected $250,000 (£135,000) in donations to take out a full-page advert in The New York Times to promote the upcoming 1.0 release of Firefox. The money will also be used for other promotional activities.
Meanwhile, Microsoft delivered some updates to Internet Explorer with Service Pack 2 (SP2) for Windows XP and is working on a new version of the browser that will ship as part of Longhorn, the codename for the next version of Windows due in 2006, Microsoft said.
Also, the Internet Explorer development team at Microsoft has emerged from obscurity by starting a web log. (http://blogs.msdn.com/ie/)
Microsoft sees the market share fluctuation as the "natural ebb and flow of a competitive marketplace", it said.
Users who try other browsers ultimately will come back to Internet Explorer, Microsoft said.
"As they check out the alternatives, we think they will discover that critical factors such as website compatibility, application compatibility and enterprise management and support are better with Internet Explorer."
Joris Evers writes for IDG News Service