CVE-2026-16399: Mozilla Firefox

High severity, CVSS 7.5. EPSS: 0.1% chance of exploitation in the next 30 days.

Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 153 and Thunderbird 153.

Affected products

• Mozilla Firefox: before 153.0.0 (fixed in 153.0.0)
• Mozilla Thunderbird: before 153.0 (fixed in 153.0)

Published 2026-07-21. Last modified 2026-07-24.