Mozilla Firefox Security

Anthropic reported that Claude Opus 4.6 found 22 Firefox security vulnerabilities during a two-week collaboration with Mozilla researchers, including 14 that Mozilla assigned as high severity. Its March 6, 2026 account describes a process in which Anthropic researchers validated findings, filed them with a description and proposed patch, and Mozilla triaged them; most issues were fixed in Firefox 148. The distinction between a crash report and a confirmed vulnerability matters: the team submitted 112 unique reports, which Anthropic says did not all turn out to be relevant to security. These counts are Anthropic's account, and the post separately reports that the exploits Claude wrote worked only in a test environment with browser protections removed.