In April 2026, Mozilla patched 423 security bugs in Firefox . Their 2025 monthly average was 21. The 20x jump wasn't a fuzzing breakthrough or a bug-bounty surge — it was the first full month of an agentic AI security pipeline running Anthropic's Claude Mythos Preview against Firefox source code. Of the 423 fixes, 271 were attributed directly to Mythos : 180 sec-high, 80 sec-moderate, 11 sec-low. They shipped in Firefox 150 (released April 21) plus dot-releases 149.0.2, 150.0.1, and 150.0.2. 📖 Read the full version with charts and embedded sources on ComputeLeap → Most coverage of Mythos this week has fixated on the offensive side — the UK AI Safety Institute's cyber-capability evaluation , the Trump administration's AI-safety reversal, and the cybersecurity-establishment debate over dual-use risk. That framing buries the more durable story.…