GoKawiilWhen 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. The researchers have also published details on 12 of the bugs, which range from a pair of unusual sandbox vulnerabilities, to a 15-year-old error in how the browser parses an HTML element.
“These things are actually just suddenly very good,” Brian Grinstead, a distinguished engineer at Mozilla, told TechCrunch. “We see that on our own internal scanning, we see that on external bug reports, and we see that in all sorts of signals across the industry.”
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