Mythos Uncovers Firefox Vulnerabilities

Mozilla announced that it applied Anthropic's Mythos to its internal security scanning and uncovered a large number of high-risk vulnerabilities in Firefox.

• In April 2026, Firefox shipped 423 bug fixes, a sharp increase from 31 in the same month a year earlier.
• 12 cases were disclosed, including 2 sandbox vulnerabilities and an HTML element parsing error that had persisted for over 15 years.
• Sandbox vulnerabilities are a category that's especially hard for AI to find, since it requires first crafting a malicious patch and then re-attacking the browser's most isolated area.
• Mozilla explained that while AI can draft patches, actual fixes still require the one engineer writes + one engineer reviews system.
• Recent AI security tools have advanced to the point where they can verify their own findings and filter out false positives, and Mozilla assessed that the way they use these tools has changed significantly over the past few months.