Saying it went too far in its pursuit of profit, the popular Internet hangout Facebook Inc. is allowing its 55 million users to permanently turn off a new marketing tool that tracks their activities at other Web sites.

The privacy control, announced in a Dec. 4 apology by Facebook founder Mark Zuckerberg, will likely limit the reach of an application called “Beacon.” The tool is part of a month-old program that the Palo Alto-based startup had hailed as an advertising breakthrough.