From WSJ:

“Even if you are logged out, Facebook still knows and can track every page you visit,” Cubrilovic wrote in a blog post about the issue. “The only solution is to delete every Facebook cookie in your browser, or to use a separate browser for Facebook interactions.” […]

Facebook acknowledges that it gets that data but says it deletes it right away. “The onus is on us is to take all the data and scrub it,” said Arturo Bejar, a Facebook director of engineering. “What really matters is what we say as a company and back it up.”

That’s certainly nice of them.