Mozilla's Firefox browser has overtaken Microsoft's Internet Explorer as the leader in Europe, the first time Microsoft's browser has lost its top spot in a major market, a web analytics firm StatCounter said.

In December, the open-source Firefox took 38.1 percent of European market share, while Internet Explorer's share slipped to 37.5 percent. Google Chrome saw its share rising to 14.6 percent from just 5.1 percent a year earlier.

This appears to be happening because Google's Chrome is stealing share from Internet Explorer while Firefox is mainly maintaining its existing share, Aodhan Cullen, StatCounter chief executive, said in a statement.

We are probably seeing the impact of the agreement between European Commission competition authorities and Microsoft, to offer EU users a choice and menu of browsers from March last year, Cullen said.

In December 2009, European Union regulators accepted Microsoft's pledge to give consumers better access to rival browsers, ending a long antitrust dispute.

Since the beginning of March, Microsoft offered Europeans the option to choose from among 12 browsers on the more than 100 million old and new PCs that use its Windows software.

Globally, Internet Explorer's share slipped to 46.9 percent in December, while Firefox was at 30.8 percent and Google was at 14.9 percent, StatCounter said.

(Editing by Sharon Lindores)

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