Yahoo achieved its highest U.S. search share in more than five years last month, according to Web traffic analytics provider StatCounter.

In December, Yahoo’s share of the U.S. search market was 10.4 percent, a jump from 8.6 percent in November. The nearly-two-point increase came at the expense of Google. From November to December, Google’s U.S. search share dropped from 77.3 percent to 75.2 percent, the lowest it’s ever been recorded by StatCounter Global Stats. Since 2008, Global Stats has been tracking global search statistics based on more than 15 billion page views on more than 3 million websites per month.

Bing’s share of the search market also increased last year, though not as significantly as Yahoo’s. From November to December, Microsoft’s search engine went from 12.1 percent to 12.5 percent. “Other” stayed relatively the same, dropping from 2 percent to 1.9 percent.

Mozilla is a significant factor in Yahoo taking part of Google’s share. For 10 years, Google was the default search engine on Mozilla’s Firefox browser, but in late November, the software company announced a five-year partnership with Yahoo. December was the first full month during which Yahoo was the default search engine on Firefox 34.

“The move by Mozilla has had a definite impact on U.S. search,” says Aodhan Cullen, chief executive at StatCounter. “The question now is whether Firefox users switch back to Google.”