Consumer advocates are raising new concerns that Google, Facebook and others are rigging an industry effort to let web browsers block Internet firms from tracking their searches by funding one of the referees in the self-policing effort.

The influential Center for Democracy and Technology, which holds one of the three chairs on the World Wide Web Consortium working up “Do Not Track” rules, received more than $2.5 million from Google, Facebook and Mozilla in recent years, according to their publicly released IRS forms.