Mozilla's advisory MFSA 2026-82 (announced 1 September 2026) lists 29 vulnerabilities fixed in Firefox 155, with an overall impact of high; Mozilla rates 13 of them high, 7 moderate and 9 low. They include sandbox escapes due to use-after-free in the DOM: Navigation (CVE-2026-84119) and DOM: Security (CVE-2026-84121) components, a privilege escalation due to use-after-free in Graphics: WebGPU (CVE-2026-84123), use-after-free flaws in the JavaScript: GC (CVE-2026-84118) and Audio/Video components, and internally found memory-safety bugs that Mozilla says showed evidence of memory corruption and that it presumes could have been exploited with enough effort.

Mozilla does not say any of them is being exploited in the wild. (source: Mozilla MFSA 2026-82)