Mozilla's AI Vulnerability Detector Uncovers 271 Firefox Flaws with Near-Perfect Accuracy

Breaking: Mozilla's Mythos AI Identifies 271 Firefox Security Holes

Mozilla announced Thursday that its AI-powered vulnerability detection tool, Mythos, has uncovered 271 security flaws in Firefox over two months—with "almost no false positives", according to engineers. The breakthrough challenges long-held skepticism about AI reliability in cybersecurity.

"[This] isn’t a lab experiment. These are real vulnerabilities that would have required months of human effort," said Mozilla's CTO in a statement. He declared last month that "zero-days are numbered" and that "defenders finally have a chance to win, decisively."

Behind the Scenes: How Mythos Worked

Mozilla used Anthropic's Mythos—an AI model fine-tuned for code analysis—combined with a custom "harness" to scan Firefox's source code. Engineers cited two key factors: improvements in the model itself and the harness's ability to guide Mythos efficiently.

"We built a system that minimizes rambling and hallucinations," explained a Mozilla security engineer. "The results speak for themselves—almost no false positives."

Background: From Skepticism to Success

Early AI vulnerability detection attempts were plagued by "unwanted slop"—plausible-sounding bug reports with hallucinated details. Human developers spent hours verifying false alarms, undermining trust in AI tools.

Critics accused companies of cherry-picking results and hyping limited successes. Mozilla's latest results, however, mark a departure—the Mythos deployment produced actionable, verified findings at scale.

What This Means for Cybersecurity

If Mythos’s success holds, it could transform vulnerability discovery. The ability to detect hundreds of flaws in weeks—with minimal false positives—could shift the balance toward defenders.

"[We] are finally at a point where AI helps us, not burdens us," said a Mozilla researcher. However, experts caution that the approach may still face challenges across different codebases and attack surfaces.

— Updated by the breaking news team