Mozilla's Firefox Web browser edged up slightly in usage at the expense of Microsoft Corp.'s (MSFT) Internet Explorer, commanding nearly 11 percent of the U.S. market on a typical weekday, according to research by WebSideStory.

On Dec. 7, Firefox had a 10.7 percent share on computers running Microsoft's Windows operating system, an increase from 9.84 percent seven weeks earlier.

By contrast, IE usage dropped to 88.2 percent, from 89.1 percent.

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Opera Software ASA's Opera and other browsers made up the rest.

Firefox's relative usage is often higher on weekends because many businesses have only IE installed on their machines, boosting Microsoft's share.

WebSideStory found growing adoption of IE 7, which Microsoft released on Oct. 18. T

he new version had 16.3 percent of overall U.S. browser usage as of Dec. 7. Firefox 2, which debuted Oct. 24, had a 3.12 percent share that day.

Combined, that means nearly one in five used a new browser.