Yet, with more than 75 percent share in December, Google still dominates search. Microsoft's Bing is a distant second, followed by Yahoo.
Google's share of the U.S. search market has dropped to its lowest level since 2009, as what appears to be the direct result of Mozilla's decision
in November to make Yahoo the default search engine on its Firefox browser.
Figures released Jan. 7 by Website analytics firm StatCounter show that Google's search market share in December dropped to 75.2 percent of all U.S. search referrals, compared with 77.3 percent in November. The latest figure represents Google's lowest since StatCounter started tracking search engine share in 2008.
Yahoo's share, meanwhile, went up from 8.6 percent in November to 10.4 percent in December. Microsoft's Bing held on comfortably to its second spot in the U.S. search market, with a 12.5 percent share, compared with 12.1 percent a month earlier.
StatCounter's numbers are based on its tracking of more than 15 billion page views from across 3 million Websites on a monthly basis. The company analyzes each page view to determine if it came from a search engine and uses this referral information to determine the popularity of various Internet browsers.
For Yahoo, last month's numbers are the company's highest since November 2009, when it accounted for an even 13 percent of search engine referrals in the United States. The spike follows Mozilla's decision to replace Google with Yahoo as the default search engine on its Firefox Internet browser.
The surprise decision last November brought to an end a decade-long partnership between Google and Mozilla that is believed to have generated hundreds of millions of dollars in royalties for Mozilla. But it appears to have opened a way for Yahoo to regain some of the ground it has lost in the search engine market over the past few years. Yahoo's latest search share numbers are certainly a lot healthier than the 5 percent market share it held as recently as last February.
With Mozilla's ending its 10-year relationship with Google and Yahoo's becoming the default search engine for Firefox 34 in the United States, there's been "a definite impact on U.S. search," Aodhan Cullen, CEO of StatCounter, said in a statement.
What remains unclear is whether Firefox users will continue to use Yahoo as their search engine of choice or whether they will go back to using Google, he added. Firefox users represented 12 percent of U.S. Internet usage in December according to StatCounter.
Google's 75 percent share continues to make it a dominating presence in the search engine market. But the company has reason to be nervous about the gains being made by its rivals. Google's search share has been gradually declining even before the Mozilla and Yahoo partnership.
StatCounter data shows that since hitting a peak of 82.3 percent in Nov. 2009, Google's share of search referrals in the United States has been slowly declining even as that of Microsoft's Bing has kept increasing. Between Nov. 2009 and Dec. 2014, Bing's share has grown from 7.4 percent to 12.1 percent while Google's share dropped more than 8 percent during the same period.
Google could be in for more bad news if Apple decides to jettison Google as the default search engine on its Safari browser, as well. Apple has a search engine partnership with Google that is scheduled to come up for renewal in early 2015. Apple is reportedly considering Yahoo and Bing as potential alternatives to Google.
While Google is still a hugely profitable and diversified company, it continues to rely heavily on its search-related advertising business. So continued declines in search engine share could spell trouble for the company over the long term.