How Anthropic’s Mythos has rewritten Firefox’s approach to cybersecurity

When Anthropic unveiled its new Mythos model in April, it also delivered a stern warning to anyone developing software. The model was so powerful at sniffing out software vulnerabilities, the lab claimed , that it had discovered thousands of high-severity bugs that would need to be fixed before it could be made public. Now, security researchers for Mozilla’s Firefox browser are providing a closer look at what that process has looked like in practice, and what Mythos’ powers mean for software security at large. In a post published on Thursday , Mozilla said Mythos has unearthed a wealth of high-severity bugs, including some that had lain dormant in the code for more than a decade. That’s a significant improvement from what AI security tools were capable of even six months ago. Until now, AI bug-finding tools have come with severe drawbacks, often inundating security teams with low quality reports and false positives . But Mozilla’s researchers say the latest generation of tools have turned a corner, particularly now that agentic systems can assess their own work and filter out bad results. “It is difficult to overstate how much this dynamic changed for us over a few short months,” the researchers wrote. “First, the models got a lot more capable. Second, we dramatically improved our techniques for harnessing these models.” Image Credits: Firefox The results are striking: In April 2026, Firefox shipped 423 bug fixes, compared to just 31 exactly a year earlier. …