Mozilla has released Firefox 159 for Windows, macOS, Linux and Android, addressing 167 security vulnerabilities while introducing improvements to password management and website monitoring.
The update, released on October 28, 2026, includes fixes for several potentially serious security weaknesses, including flaws that could allow attackers to execute malicious code or escape the browser's security sandbox.
Mozilla has also enabled its sidebar password manager by default and begun gradually introducing Smart Window, a feature designed to monitor websites for changes.
The next major browser update, Firefox 160, is scheduled for November 10, 2026.
Firefox 159 Addresses 108 High Risk Security Vulnerabilities
Security improvements are the most significant part of Firefox 159.
Mozilla has resolved 167 vulnerabilities, including 65 reported by external security researchers. Amy Burnett from OpenAI contributed seven vulnerability reports.
Of the vulnerabilities addressed, 108 are classified as high risk, 52 as medium risk and seven as low risk.
The update also fixes 97 use after free vulnerabilities. These flaws occur when software attempts to access memory after it has already been released, potentially allowing attackers to trigger crashes or execute malicious code.
Another 13 vulnerabilities could allow attackers to escape Firefox's sandbox, a security mechanism designed to restrict potentially harmful browser processes.
| Security category | Number of vulnerabilities |
|---|---|
| High risk | 108 |
| Medium risk | 52 |
| Low risk | 7 |
| Total fixed | 167 |
Firefox 159 Enables Sidebar Password Manager by Default
Alongside security improvements, Firefox 159 changes how saved passwords can be accessed.
The browser's password management tool now appears in the sidebar by default, removing the need to manually enable it.
Interestingly, the feature is available even when you do not store passwords in Firefox.
Mozilla is also gradually introducing Smart Window, an AI assisted feature that monitors websites for changes.
It can help identify updates such as newly published blog posts or changes in product prices.
However, the rollout is taking place in stages, meaning the feature may not immediately appear for everyone.
Firefox ESR Versions Also Receive Security Updates
Mozilla has released security updates for its Extended Support Release editions alongside Firefox 159.
Firefox ESR 153.6.0 addresses 145 vulnerabilities, while Firefox ESR 115.44 resolves 80.
Firefox ESR 115.44 continues to support older operating systems, including Windows 7, Windows 8.1 and macOS 10.12 through 10.14.
Mozilla plans to maintain that older platform support until March 2027.
These ESR releases address vulnerabilities relevant to their respective browser versions rather than including every fix from Firefox 159.
Given the number of high risk vulnerabilities resolved, installing the latest compatible Firefox update is advisable.
You can check your installed version through Firefox's About menu, which also allows the browser to check for available updates.
Firefox 159 is available now, with additional improvements expected when Firefox 160 arrives in November.
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