Anthropic's Claude Mythos Found 271 Vulnerabilities in Mozilla Firefox: New 150 Release Fixes Them

Mozilla has officially launched Firefox 150, featuring a massive 271 security patches identified through Anthropic's Claude Mythos AI. This version introduces significant productivity upgrades, including an advanced Split View, a full-featured PDF editor, and real-time translations.

It seems that finding vulnerabilities in Firefox is becoming a kind of benchmark for Anthropic's new AI models. In March, the company announced Claude 4.6, boasting of having found multiple high-severity vulnerabilities in the browser. Now, Anthropic is back at it again, this time with the powerful Claude Mythos Preview, which helped uncover a staggering 271 security vulnerabilities in Mozilla Firefox. The browser's creator is releasing update 150 to patch these security holes and improve other aspects.

Claude Mythos found 271 flaws in Firefox; the 150 release fixes them

According to Mozilla, the AI model acted as a force multiplier for their human researchers. Mythos was able to identify flaws ranging from minor bugs to high-severity risks quickly. It reportedly showed great capabilities in source code analysis at a pace impossible for people. This efficiency allowed the team to "round the curve" of security debt, fixing in weeks what traditionally would have taken months of expensive manual labor.

The use of Anthropic's model represents a turning point for cybersecurity. Bobby Holley, Firefox's CTO, noted that the tools have fundamentally changed the game. He claims Mythos offers automated techniques that cover the full spectrum of potential bugs. This level of analysis was previously reserved for elite researchers or well-funded attackers. Now, AI is tilting the balance back toward the defenders.

Interestingly, the AI didn't find categories of bugs that humans couldn't eventually see. Instead, it provided a "firehose" of discoveries that required a disciplined response from Mozilla's engineers.

Productivity features get a major lift

Beyond the invisible security wall, Firefox 150 introduces tangible improvements for the daily user. The Split View feature, which allows side-by-side browsing, is now more intuitive. Users can right-click any link to open it directly in a split window without losing their place on the original page. This mode also supports tab searching and simple window reordering for better multitasking.

Tab management and document handling got some nice upgrades. A new sharing function lets you select multiple tabs at once and copy their titles and URLs in a single action. This makes it easier to move workflows between apps. Additionally, the PDF editor is now more "Pro" than ever. It lets users reorder pages by dragging thumbnails, delete sections, or export individual pages as separate files.

Translation is another area where Firefox is becoming more self-sufficient. Users can now access real-time translations -- via a dedicated internal page -- that rival popular standalone services. This tool can automatically figure out what language you're using and lets you quickly change text right in the browser. In other words, you won't need to install third-party extensions to use the feature.