AI Finds 271 Security Flaws in Firefox Browser

Imagine a digital security guard that never sleeps, never gets tired, and can spot dangers four times faster than an entire year's worth of human experts. That's exactly what just happened at Mozilla Firefox.

Anthropic's AI model, Claude Mythos Preview, scanned Firefox's code and uncovered 271 security vulnerabilities in a single evaluation. All of them have been fixed in this week's Firefox 150 update, protecting millions of users worldwide.

To understand how remarkable this is, consider that Mozilla addressed about 73 high-severity vulnerabilities in all of 2025. This AI found nearly four times that number in one go.

The partnership between Mozilla and Anthropic started in February 2026. An earlier AI model found 22 vulnerabilities in two weeks, with 14 classified as high-severity. Those fixes shipped in Firefox 148, proving the concept could work.

But Claude Mythos took things to an entirely new level. The AI works autonomously, finding and understanding vulnerabilities across major operating systems and browsers without human guidance after the initial setup.

The model's power extends beyond Firefox too. It discovered a 27-year-old bug in OpenBSD, a 16-year-old flaw in FFmpeg, and a 17-year-old vulnerability in FreeBSD. These ancient problems had hidden in plain sight through decades of human review.

The Bright Side

For years, cybersecurity experts have accepted a frustrating reality: attackers only need to find one weakness, while defenders must protect everything. The odds have always favored the bad guys.

AI tools like Claude Mythos are finally evening the playing field. Defenders can now discover vulnerabilities quickly, systematically, and affordably before attackers exploit them.

Mozilla engineers say this collaboration represents a turning point. The long-held belief that perfect security is impossible might finally be challenged.

What makes this truly hopeful is the speed and accessibility. Instead of waiting months or years for security researchers to manually review millions of lines of code, AI can do it in days while human experts focus on fixing what it finds.

As these AI tools become more widely available to defenders, the internet could become genuinely safer for everyone who uses it.