The impressive figure encompasses all downloads of the browser since its release in 2004.  More interestingly, W3Schools.com, an internet research firm, is reporting Firefox to have seized 47.9 percent of the market, jumping ahead of Internet Explorer, which it says has a combined marketshare of 39.4 percent for versions 6, 7, and 8.

More conservative StatCounter, another research firm, puts Mozilla's marketshare at 32 percent, while putting Internet Explorer's at just about 60 percent.  Both firms' figures are suspect due to inherent difficulties in determining true browser marketshare.  Most firms collect metrics from a broad array of sites, but even collecting from as many as 1,000 sites two firms may show great differences in market pictures, due in part to different kinds of user populations for their surveyed sites.  Furthermore, W3School's analysis is mostly of tech-related websites, which are visited more by the kinds of users who would use alternative browsers at a higher rate.

Mozilla does have tough competition for the title of full-standards third-party browser king.  Opera, Google's Chrome, and Apple's Safari all strive for the title.  However, all of these competitors are dwarfed by Mozilla in the PC market, with a mere 5 percent of this total market, according to StatCounter.  Meanwhile Microsoft still enjoys a healthy lead of approximately 60 percent.

Firefox 3.5's popularity comes thanks largely to its strong support of standards.  Like Opera and others, Firefox features support for SVG graphics and other modern standards -- many of which are not supported by Internet Explorer 8's default install.  The browser also features brand new standards such as HTML 5, which is viewed as a possible non-proprietary successor to Adobe's Flash and Microsoft's Silverlight rich web platforms.  HTML 5 features support for videos among other things.

Mozilla, Opera, and others should enjoy a healthy boost overseas if Microsoft's offer to include a ballot screen in Windows 7 is accepted by the EU.  The move, designed to fulfill antitrust compliance, would allow users to pick between IE 8, Firefox, Opera, Chrome, and Safari upon installation of Windows 7.

In honor of the billion dowloads mark, Mozilla has launched a new promotional website OneBillionPlusYou.com.  It is also hard at work, preparing iterative updates 3.6 and 3.7, which showcase new themes.  It also is working on Firefox 4.0, which should raise the bar even higher.