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.”

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.