What Mozilla learned running an AI security bug hunting pipeline on Firefox

Over the past several months, Mozilla ran an agentic harness powered by Claude Mythos Preview across Firefox’s source code, identifying 271 security bugs that were fixed in Firefox 150, with additional fixes shipped in versions 149.0.2 and 150.0.1. Over 100 people contributed code to get those patches out. The bugs spanned a wide range of subsystems.