Yahoo, Inc. announced Wednesday that it had reached a deal with Mozilla to become Firefox's default search engine, reports Reuters.

"I'm thrilled to announce that we've entered into a five-year partnership with Mozilla to make Yahoo the default search experience on Firefox across mobile and desktop," said Yahoo CEO Marissa Mayer. "This is the most significant partnership for Yahoo in five years and we're so proud that Mozilla has chosen us as their long-term partner in search."

The deal starts on December this year after Mozilla Corp. ends its contract with Google this November. Yahoo said the partnership with Mozilla will last five years, but failed to clarify how it could affect their own partnership with Microsoft. Yahoo's search capabilities is currently powered by Bing, Microsoft's search engine.

Firefox users in the United States will be the first to experience the change, as the new search engine shows up in December this year. Yahoo promises a "a clean, modern, and immersive search experience" that will also make its appearance for all Firefox users early in 2015.

"Firefox is a major source of the search traffic that's Google's bread and butter," writes Stephen Shankland of CNET. Mozilla Corp.'s primary source of income comes from a share of the profits gained from Google's advertising network. The company's $311 million income in 2012 alone was generated hugely by advertising revenue.

"Google now has Chrome, though, and it doesn't have to share search-ad revenue from that browser with anybody but itself," writes Shankland.

As Chris Beard, Mozilla's CEO, explained, "Google has been the Firefox global search default since 2004. Our agreement came up for renewal this year, and we took this as an opportunity to review our competitive strategy and explore our options."

"Today we are announcing a change to our strategy for Firefox search partnerships. We are ending our practice of having a single global default search provider. We are adopting a more local and flexible approach to increase choice and innovation on the Web, with new and expanded search partnerships by country," Beard added.

Beard also explained that Firefox will continue to have Google, Bing, DuckDuckGo, eBay, Amazon, Twitter and Wikipedia as alternative search engines in the U.S., while Firefox users in other countries will have different options, such as Yandex Search for Russia and Baidu for China.