Firefox 150: Anthropic's Mythos Revolutionizes Vulnerability Hunting

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Key Takeaways

1Mozilla collaborated with Anthropic's Mythos AI to identify 271 vulnerabilities in Firefox 150, marking a turning point in cybersecurity.

2This advancement could put an end to "zero-day" attacks, shifting the balance of power between hackers and defenders.

3Mythos outperformed the previous model Opus 4.6, which had only fixed 22 vulnerabilities in Firefox 148.

💡Why it matters — Mythos's ability to massively detect vulnerabilities could transform software security, reducing the risks of exploitation by cybercriminals.

An Unprecedented Collaboration for a Major Advancement

Mozilla has recently teamed up with the artificial intelligence Mythos, developed by Anthropic, to enhance the security of its Firefox browser. This collaboration has led to the discovery and correction of 271 vulnerabilities in version 150 of Firefox. Mozilla hopes that this advancement will mark the beginning of the end for so-called “zero-day” attacks, which exploit flaws unknown to developers. Although Mythos is extremely effective, its access is restricted to a few selected organizations due to its sensitivity.

Discreet but Revolutionary Updates

Beneath the appearance of mundane updates, version 150 of Firefox, released on April 21, 2026, conceals a true revolution in cybersecurity. Indeed, thanks to Anthropic's AI, Mozilla was able to identify nearly 300 flaws in record time. This advancement could very well reverse the traditional power dynamic between hackers and web defenders.

The release notes for Firefox 150 mention features like split view and enhancements for the integrated PDF editor. However, the real change lies in the use of AI to track vulnerabilities, as revealed in a blog post published on the same day.

In-Depth Cleanup Thanks to AI

In a blog post with an evocative title, Bobby Holley, a member of the Firefox development team, unveiled the details of this collaboration with Anthropic. The AI model Mythos played a crucial role. Compared to a previous cooperation with the Opus 4.6 model, which had corrected 22 flaws in Firefox 148, Mythos identified and corrected 271 vulnerabilities in Firefox 150, achieving an efficiency increase of twelve times.

Bobby Holley believes that thanks to this efficiency, zero-day flaws could soon belong to the past. These vulnerabilities are particularly dangerous as they are exploited by hackers even before developers are aware of them.

Rebalancing the Fight Against Cyberattacks

The discovery of nearly 300 flaws has raised some concern within Mozilla's teams. Even with rigorous maintenance, such a number of vulnerabilities is surprising. “For a well-protected target, just one of these bugs would have triggered a red alert in 2025,” explains Mozilla. Given such a quantity, it is legitimate to wonder if the pace can be maintained.

However, the effectiveness of Mythos is seen as an opportunity to rebalance a fight that is often asymmetric, typically favoring the attackers. Bobby Holley asserts that this experience is a source of hope for the teams, who, after overcoming the initial shock, can return to work with a new perspective.

Towards a New Era of Cybersecurity

Mozilla chooses to see the positive side of this situation. There is “light at the end of the tunnel” for cybersecurity. Hackers have long taken advantage of traditional software's inability to detect complex flaws. With the automation of this expertise through AI, the historical advantage of attackers is beginning to erode.

The Mozilla team wants to reassure: the AI does not discover “extraterrestrial” vulnerabilities beyond human intelligence. All 271 flaws could have been detected by a high-level expert, but Mythos allows this to be done on an industrial scale.

Bobby Holley concludes optimistically: “Defects are limited in number, and we are entering a world where we can finally find them all.”