StatCounter, a Web tracking service, published data over the weekend claiming that Microsoft's Internet Explorer browser is losing ground.

Whether the data will hold remains to be seen. The trend has not yet been confirmed by other tracking services, leading some bloggers to question whether the data is a blip or whether Microsoft's rivals -- Mozilla, Apple's Safari, and Google's Chrome are truly making gains.

Mozilla released version 3.5 of its popular Firefox browser June 30th.

Microsoft's most recent version of its browser -- Internet Explorer 8, which is offered through Windows Update as part of Microsoft's regular security upgrades -- has been growing steadily, according to StatCounter, gaining nearly 17 percent marketshare since it was released in March.

Internet Explorer 7, however, has dropped more than that, according to StatCounter. It shed 19 percentage points since March -- down to 30 percent from 49 percent, while Internet Explorer 6 holds less than 8 percent of the market.

According to math done by TechCrunch, a Silicon Valley blog, Internet Explorer's share for all three versions is now 54.4 percent, down from 65.8 percent in March.

Net Applications, another Web tracking firm, hasn't released its latest data on browsers and said in May that usage of Internet Explorer 8 may be under-reported because of a new Microsoft feature called "compatibility view," which displays Web pages in Internet Explorer 8 as if they were in Internet Explorer 7.

Until mid-May, Net Applications was counting all of those pages -- about a fifth of the sampling it was doing for Internet Explorer 8 -- as Internet Explorer 7, the company said. It is now reporting those pages as being in "Internet Explorer 8 compatibility mode."

StatCounter's data also shows that Mozilla's Firefox is gaining ground. The open source browser now holds over 27 percent of the market, according to StatCounter, second only to Internet Explorer 7, and Mozilla released another upgrade, Firefox 3.5, last week.

In the last year, Mozilla's engineers have been working on executing code faster, Mozilla Foundation board member Mitch Kapor told the San Francisco Chronicle in December, in an effort to bring more for-profit discipline to the open source effort.

Other Microsoft browser competitors -- including Firefox 2, Apple Safari and Google Chrome -- hold less than 10 percent of the market even when combined.

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