It represents the first acquisition in Facebook's three-year history. Financial terms weren't disclosed.
Mountain View-based Parakey consists of just two people, Blake Ross and Joe Hewitt, who are best known for their contributions to the open-source initiative that created Firefox - the second most-used Web browser behind Microsoft Corp.'s Internet Explorer.
Ross and Hewitt will both go to work for Palo Alto-based Facebook, which is trying to turn its site into a melting pot of software applications and features contributed by software developers eager to reach its network of 31 million users.
''We are thrilled to join the most innovative technology company in the industry,'' Ross said.
Parakey had been trying to bridge the gap between information hosted on the Web and data stored on computer hard drives.
Privately held Facebook ranks among the Web's fastest growing sites. News Corp.'s MySpace is the only social networking site that is larger.
The Parakey acquisition is the latest indication that Facebook's 23-year-old chief executive, Mark Zuckerberg, intends to keep building the company instead of selling to one of its many suitors.
Yahoo Inc. offered to buy Facebook for about $1 billion last year, only to be rebuffed.
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