Xmarks, formerly Foxmarks, was a San Francisco-based company which produced an add-on to web browsers, which is also entitled Xmarks. The company was founded in 2006 by Mitch Kapor and was acquired by LastPass in December 2010

How to remove Xmarks account

Be logged in and use the removal link named here.
Direct removal link: http://login.xmarks.com/account/delete_account