An attacker had compromised Mozilla’s bug tracker and testing tool Bugzilla, and used the stolen security-sensitive information to attack Firefox users, Mozilla warned in a blog post.

In an FAQ published along with the blog post, Mozilla added that a privileged user account was compromised by the hacker. The user reused the password on another website, which suffered a data breach. Then attacker gained accessed to Bugzilla account and downloaded security-sensitive information about the flaws in Firefox and other Mozilla products.