Today, Yahoo and Mozilla announced a five-year partnership that would make Yahoo the default US search engine for Mozilla's Firefox browser on mobile and desktop. In December, Yahoo will roll out an enhanced new search function to Firefox users, and will also support Do Not Track functions in Firefox as a result of the partnership. The agreement also sets the stage for future product integrations, but so far the companies are keeping quiet on what those might be. Firefox has lost market share in recent years but is still used by roughly 17 percent of webgoers. According to Mozilla CEO Chris Beard, Firefox users search the web more than 100 billion times each year, suggesting a major windfall for Yahoo as a result of the deal.

"An opportunity to review our competitive strategy."

By comparison, only 10 percent of web searches are made through Yahoo, which is powered by Microsoft Bing. But Google and Bing have both made major gains in recent years. Nonetheless, Yahoo CEO Marissa Mayer said search traffic is still a major priority for the network, and one they expect to explore through the new partnership. "At Yahoo, we believe deeply in search – it’s an area of investment, opportunity and growth for us," said Mayer. "I can’t wait to see what innovations we build together."

Google has been Firefox's default browser for ten years, so the new partnership represents a significant break. In a subsequent blog post, Mozilla CEO Chris Beard described the decision as a strategic one. "Our agreement came up for renewal this year, and we took this as an opportunity to review our competitive strategy," Beard wrote. "We believe it will empower more people, in more places with more choice and opportunity to innovate and ultimately put even more people in control over their lives online." Mozilla is also setting Yandex as the default search engine in Russia, and the move opens up the company to work with more local partners. Google, Bing, DuckDuckGo, eBay, Amazon, Twitter and Wikipedia will continue as alternative search options in the US.

11/19 5:11pm ET: Updated to include Beard statement