As Facebook CEO Mark Zuckerberg prepared to face nearly half of the Senate today to explain what went wrong with his company’s handling of personal data for millions of Facebook users, the Mozilla Foundation released a report that highlights the dangers posed to the entirety of the Internet ecosystem by the increasing concentration of control over how people experience the online world in the hands of companies like his.

Zuckerberg opened his remarks today by saying, “Facebook is an idealistic and optimistic company” and that he and others believed that the tools Facebook created were a force for good. “It’s clear now that we didn’t do enough to prevent those tools from being used for harm as well,” he admitted. The danger that Facebook executives overlooked, however, is described clearly by the Mozilla Foundation report.