Meanwhile, 's posted a record gain that brought it close to a 10% share for the first time since began tracking operating system use.

In December, 88.7% of the people who browsed the Web sites that Net Applications monitors did so using machines powered by Windows, a 0.94 percentage point drop from November. The slide was Windows' largest in the four years that Net Applications has collected operating system data, and the second record-setting monthly loss in a row for Microsoft's software.

During November, Windows' market share slipped 0.84 percentage point, dropping the operating system since Net Applications has been tracking OS use.

The combined decline of November and December totaled 1.8 percentage points, Windows' biggest two-month dip ever, nearly double that of its previous record, a 0.92 percentage point fall in December 2007 and January 2008.

Microsoft's OS ended the year down 3.1 percentage points, a 3.4% drop in its share from the same time last year.