In the last two months, however, Yahoo's U.S. search share has slipped slightly, losing three-tenths of a percentage point, according to measurement firm comScore.
After a January peak of 13%, Yahoo's search share dropped in February to 12.8%, then shed share again, ending March with 12.7%, data recently released by comScore showed.
Mozilla changed the default search from Google to Yahoo when it released Firefox 34 on Dec. 1, 2014. The Mozilla-Yahoo deal was a result of the former not renewing its long-standing partnership with Google, which in 2013 generated approximately $275 million in revenue for Firefox's developer.
Firefox continues to use Google as the default search engine in many markets, including much of Europe.
Before the two struck a partnership, Yahoo's U.S. search share was 10.2%. The recent slippage may be a result of Google's efforts to bring Firefox users back.
Google began those entreaties soon after the Mozilla-Yahoo deal went into effect. In January, Google asked Firefox users whether they wanted to reset their home page or change their default search engine to Google. Those appeals appeared in small banners atop the google.com page, not within the search results.
Something similar continues to appear at the top of google.com when Firefox is steered there. "Get to Google faster. Switch your default search engine to Google," the banner read today.
Last month, Google began embedding a prominent plea above its search results in Firefox: The appeal appeared after executing a search from google.com in Firefox when the browser had Yahoo as its default provider.
"Switch your default search engine to Google," the alert stated. When users clicked the offered "Learn how" button, they saw instructions for changing the provider.
Google continues to use that tactic as well.