security
Apr 29, 2026
By Teun
Firefox 150 Fixes 271 Vulnerabilities Found by Claude Mythos
Firefox 150 includes fixes for 271 vulnerabilities found during an early evaluation of Anthropic’s Claude Mythos Preview, according to Mozilla. The company said the findings came from continued collaboration with Anthropic after an earlier scan with Opus 4.6 led to 22 fixes in Firefox 148.
Mozilla said Firefox 150 ships with fixes for 271 vulnerabilities identified during an early evaluation of Anthropic’s Claude Mythos Preview. The findings came from a continued effort to scan the browser with frontier AI models and patch issues before they could be abused.
The company said this work follows an earlier collaboration with Anthropic that used Opus 4.6 to inspect Firefox. That earlier effort led to fixes for 22 security-sensitive bugs in Firefox 148, according to Mozilla. The latest round went further, with the early Claude Mythos Preview evaluation surfacing 271 vulnerabilities that are now addressed in Firefox 150.
⚡ New to this?
This matters because a browser is one of the main places people handle passwords, emails, company tools, and web apps. A vulnerability is a software flaw that could let an attacker misuse the browser, and a zero-day is a flaw known before many people have had a chance to fix it.
Mozilla says AI models helped find a large number of these flaws in Firefox, which shows how security testing is changing. For non-experts, the big point is that defenders now have another tool for finding bugs faster, but only if updates reach users quickly.
🦞 OpenClaw angle
If you run self-hosted AI agents for security work, treat browser and dependency scanning as a continuous job, not a one-off audit. Use AI-assisted review to generate findings, then route them into a human triage step so you can separate likely exploitable issues from low-priority noise.
Make patch deployment part of the same workflow. If your agents find a high-risk flaw, your automation should open the ticket, attach evidence, and trigger the fastest approved update path so fixes do not sit waiting for manual scheduling.
Mozilla described the pace of the findings as unusually high. The company said that for a hardened target, even one bug could have been treated as a serious alert in 2025, and that finding so many at once was enough to make defenders pause and reassess priorities.
The browser maker said the experience has been encouraging for security teams. According to Mozilla, the work showed that defenders who focus on identifying and fixing latent flaws can make real progress, even if it requires putting other tasks aside for a time.
Mozilla also said the work is not finished. But the company framed the latest release as evidence that the approach is already changing the balance in favor of defenders, assuming they can patch quickly and get updates out to users without delay.
The announcement highlights how AI-assisted security scanning is being used in a real production browser, not just in lab tests. Firefox is one of the most widely used open-source browsers, so vulnerabilities in it can affect a large number of users if they are left unpatched.
The company did not say the 271 issues were all exploitable in the same way, only that they were vulnerabilities identified during the evaluation and fixed in the new release. Mozilla’s message was that the combination of AI-assisted discovery and rapid patching can expose far more weaknesses than traditional review alone.
The release of Firefox 150 is the latest result of that effort, with fixes for the 271 vulnerabilities identified in the Claude Mythos Preview evaluation.
