Mozilla patched 271 Firefox bugs found by Anthropic’s Mythos, and says the zero-day era has an expiration date

Summary: Mozilla released Firefox 150 with fixes for 271 security vulnerabilities identified by Anthropic’s Claude Mythos Preview, an unreleased frontier AI model distributed under the restricted Project Glasswing programme. The collaboration began with Claude Opus 4.6 finding 22 bugs in Firefox 148 earlier this year; Mythos produced more than twelve times as many. Firefox CTO Bobby Holley said the defects are “finite” and that defenders can “finally find them all,” while the UK AI Security Institute confirmed Mythos can also execute autonomous multi-stage network attacks, making the dual-use tension the central policy question.

Mozilla released Firefox 150 on Monday with fixes for 271 security vulnerabilities identified by Anthropic’s Claude Mythos Preview, an unreleased frontier AI model restricted to a handful of organisations under Project Glasswing. The number is striking not because the bugs were exotic but because they were not. “We haven’t seen any bugs that ...