Ross announced the move on Facebook and Twitter late Thursday, saying he would spend part of his time at the ride-hailing firm working on product strategy and growth, “and the rest on non-tech projects.”

In his Facebook post, Ross quipped that part of his job would be to “rally the troops and improve my passenger rating.”

Ross was the lead architect on Mozilla’s Firefox browser, which was once the primary challenger to Microsoft’s Internet Explorer—these days it has around 6% share of the global browser market, which is dominated by Google’s Chrome.

Perhaps more relevantly to his new post, Ross worked for Facebook between 2007 and 2013, starting as an engineer who was brought in when Facebook bought his “web operating system” company Parakey. He went on to co-found the company’s growth team and worked his way up to director of product.

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The news of Ross’s hiring comes days after Uber unveiled former Expedia chief Dara Khosrowshahi as its new CEO, replacing Travis Kalanick, who was ousted after a series of company scandals and a family tragedy.

With Uber facing many challenges beyond its internal turmoil, from increasingly strong international rivals to the ongoing threat of regulation, its management team has a lot of work cut out for it ahead of a potential IPO in the next few years.