Firefox 148.0

Claude Opus 4.6 Discovers 22 Firefox Vulnerabilities in Two-Week Mozilla Partnership

Anthropic's Claude Opus 4.6 identified 22 vulnerabilities in Firefox over two weeks in February 2026, of which Mozilla classified 14 as high-severity—representing nearly a fifth of all high-severity Firefox vulnerabilities remediated in 2025. The collaboration grew from internal evaluations showing Opus 4.5 was near-saturating CyberGym, a benchmark for LLM security capability, prompting Anthropic to test against a harder real-world target. Claude scanned nearly 6,000 C++ files and submitted 112 unique reports, with most issues patched in Firefox 148.0. The effort also included an evaluation of Claude's ability to write primitive exploits, probing the upper limits of AI-enabled offensive security capability.