BERLIN — For the first time in a decade, Microsoft’s Internet Explorer is no longer the leading Web browser in Europe, ceding the position to Mozilla’s Firefox, an Irish research company that tracks Web use said Tuesday.

While three research companies also active in the field disputed the finding, StatCounter, a company in Dublin, said that Firefox surpassed Internet Explorer as the top European browser in December, with a 38.1 percent share, compared with Explorer’s 37.5 percent.

“This is a watershed event for Europe,” said Aodhan Cullen, StatCounter’s chief executive and founder.

Cullen said Microsoft had lost market share mainly to Google’s Chrome browser, whose share rose to 14.6 percent from 5.1 percent a year earlier.

Internet Explorer is still the leader worldwide, with a 46.9 percent share in December, versus 30.8 percent for Firefox and 14.9 percent for Google, StatCounter said.

Barbara Huppe, a Mozilla spokeswoman in Berlin, said that her company tended to follow other studies more closely, which still placed Microsoft ahead of Firefox in Europe. But she said the StatCounter ranking showed the market was tightening.

“This is very positive for us,” Huppe said. “We have been the top browser in Germany, the biggest European market, since 2010. That has helped us a lot.”