Anthropic's Claude Mythos Preview uncovered 271 previously unknown security vulnerabilities in Firefox 150, including bugs up to 20 years old. Mozilla describes an agentic pipeline where the AI builds and runs its own test cases to filter out false positives. Going forward, every new piece of code is to be automatically checked before commit.

New details about what we found, and how agentic harnesses are now able to reproduce real bugs and dismiss false positives.

The developer of Firefox says it has "completely bought in" on AI-assisted bug discovery.