
Mozilla applied Claude Mythos Preview to Firefox and found 271 vulnerabilities. All of them are fixed in Firefox 150, which shipped this week.
For context: when Mozilla used Claude Opus 4.6 on Firefox 148, it found 22 bugs. Mythos found 271 in the next version.
Mozilla's CTO described the experience as giving the team "vertigo." For a hardened target, one zero-day would have been a red alert in 2025.
The more important line from Mozilla: they found no category of vulnerability that humans can find that Mythos cannot.
Security has always favored attackers because finding one bug is easier than defending against all of them. AI just changed that equation - for both sides.
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