Facebook is strengthening its product development team at the expense of Mozilla, whose vice president of engineering will join Mark Zuckerberg's social networking company.

Mike Schroepfer, a leader in the development of Mozilla's Firefox browser and a former Sun Microsystems CTO, has accepted a job as engineering director with Facebook and will start in a few weeks, Facebook said Monday.

Schroepfer's position is a new one. One of four Facebook engineering directors, he will focus on front-end product and platform engineering and will report directly to Zuckerberg, Facebook's founder and CEO.

At Sun, Schroepfer was CTO of its data-center automation division and became a distinguished engineer. He arrived at Sun when the company acquired CenterRun, where Schroepfer was founder and chief architect and engineering director.

Facebook needs all the high-level engineering help it can get as it attempts to retain and attract subscribers by providing new and enhanced social networking features and to take its application platform to the next level as developers' expectations and competing options continue to rise.

Facebook's new services have been hit-and-miss in the past year or so, ranging from disappointing introductions, like its Beacon ad program, to well-received, albeit far from perfect, efforts like its developer program.

Facebook has a lot of opportunity to improve its core subscriber services, like photo management, search and messaging, while it continues to tweak its application development program to promote truly useful applications and weed out spammy and generally pointless ones.

At the same time, competition has heated up not only from traditional rivals like MySpace but also from new ones, like Google, which has significantly increased its attention on the social networking market, and like microblogging phenoms Twitter and FriendFeed.

For example, OpenSocial, a project launched by Google and now supported by a variety of players, including MySpace and Yahoo but not Facebook, is seen as a competitive reaction to Facebook's application platform. Google and Facebook also recently locked horns over their respective data portability efforts.

Meanwhile, Facebook is rolling out a significant redesign of its user interface, in part intended to highlight the short, spontaneous and frequent messages and updates that have made Twitter and FriendFeed so popular.