Critical (9.8) in mozilla. EPSS 0.7% chance of exploitation in the next 30 days.
A flaw in handling fullscreen transitions may have inadvertently caused the application to become stuck in fullscreen mode when a modal dialog was opened during the transition. This issue left users unable to exit fullscreen mode using standard actions like pressing "Esc" or accessing right-click menus, resulting in a disrupted browsing experience until the browser is restarted.
*This bug only affects the application when running on macOS. Other operating systems are unaffected.* This vulnerability affects Firefox < 133, Firefox ESR < 128.5, Thunderbird < 133, and Thunderbird < 128.5.
Severity
CVSS 3.1
9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS
0.7% chance of exploitation in the next 30 days; higher than 52% of CVEs (scores of 2026-10-31)