By Daniel Hunter
Yahoo will replace Google as the default search engine used on Mozilla Firefox web browser in the US.
Google has been the default engine on Firefox for a decade, but with the deal coming to an end, Firefox turned to Yahoo. Yahoo said it will produce a "clean, modern and immersive design" to be launched in December.
The deal will last for five years.
Yahoo chief executive Marisa Mayer said it was "the most significant partnership for Yahoo in five years".
"At Yahoo, we believe deeply in search - it's an area of investment and opportunity for us."
Firefox accounts for roughly 10% of web browsers used in the US and Yahoo is used for around 10% of searches. By contrast, Google dominates both markets with a 67% share of searches and 33% of web browsers with Google Chrome.
"Our new search strategy doubles down on our commitment to make Firefox a browser for everyone, with more choice and opportunity for innovation," said Mozilla chief executive Chris Beard.