Mythos found 271 Firefox flaws – but none a human couldn’t spot

The Mozilla Foundation has revealed it tested Anthropic’s bug-finding “Mythos” AI model and feels the results it experienced represent a watershed moment for software defenders.

The FOSS outfit on Tuesday reminded readers that it used Anthropic’s Opus 4.6 model to look for bugs in Firefox 148 and found 22 bugs.

Mythos found 271 vulnerabilities in Firefox 150.

Mozilla CTO Bobby Holley expressed mixed feelings about that result, which he described as giving the Firefox team “vertigo” as they confronted the need to fix so many flaws.

“For a hardened target, just one such bug would have been red-alert in 2025, and so many at once makes you stop to wonder whether it’s even possible to keep up,” he wrote.

He also thinks the huge haul of bugs Mythos identified represent “light at the end of the tunnel” for security teams.

“Our work isn’t finished, but ...