Last year, the FBI used a zero-day flaw to hack TOR browser and de-anonymize users visiting child sex websites. Mozilla is requesting the government to ask the FBI about the details of the hack so that it can ensure the security of its Firefox browser. TOR is an anonymity software that provides a safe haven to human rights activists, government, journalists and journalists but also is a place where drugs, child pornography, assassins for hire and other illegal activities has allegedly been traded. Mozilla wants time to analyze the vulnerability, prepare a patch, and update its products before any malicious actor could exploit the flaw.
Source: https://thehackernews.com/2016/05/fbi-tor-firefox.html