As part of a security collaboration with Mozilla, Anthropic announced on Friday that it has found 22 new security flaws in the Firefox web browser.
Of these, one has been evaluated as low severity, seven as moderate, and fourteen as high. Firefox 148, which was updated late last month, fixed the problems. In January 2026, the vulnerabilities were discovered over the course of two weeks.
According to the artificial intelligence (AI) company, “almost a fifth” of the high-severity vulnerabilities that were fixed in Firefox in 2025 were found by its Claude Opus 4.6 large language model (LLM).
After “just” 20 minutes of investigation, according to Anthropic, the LLM found a use-after-free problem in the browser’s JavaScript. A human researcher verified the findings in a virtualized environment read more about Anthropic Finds 22 Firefox Vulnerabilities Using Claude Opus 4.6 AI Model.
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