Mozilla Releases Firefox 153 Fixing 63 Vulnerabilities Including Critical ESR Issues

Mozilla Foundation released Firefox 153 on July 21, 2026, addressing a total of 63 vulnerabilities tracked under CVE identifiers. The update also covers the Firefox ESR branch, where several flaws already had public exploit code available, earning a Critical severity rating. Among the High-severity issues resolved are same-origin policy bypasses in navigation handling such as CVE-2026-16349 and multiple memory-safety problems. The release further patches Use-After-Free vulnerabilities including CVE-2026-16362 and several sandbox escape flaws designated CVE-2026-16351, CVE-2026-16352, CVE-2026-16356, and CVE-2026-16367. Additional fixes cover boundary condition errors, integer overflows, miscompilation issues, privilege escalation vectors, and information disclosure problems. In total the advisory lists 20 High, 35 Moderate, and 8 Low severity vulnerabilities that have been mitigated.

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Mozilla Foundation has released Firefox 153 along with an updated Firefox ESR branch on July 21, 2026, resolving multiple security vulnerabilities.

The stable channel update addresses 63 CVEs and is rated High overall, while the ESR version fixes publicly exploitable flaws classified as Critical.

Twenty of the issues carry a High severity rating. These include a same-origin policy bypass in navigation handling tracked as CVE-2026-16349 and several memory-safety vulnerabilities.

Additional High-severity fixes cover a Use-After-Free flaw (CVE-2026-16362) and multiple sandbox escape vulnerabilities: CVE-2026-16351, CVE-2026-16352, CVE-2026-16356, and CVE-2026-16367.

The advisory also resolves boundary-condition errors, integer overflows, miscompilation problems, privilege-escalation vectors, and information-disclosure issues.

Thirty-five Moderate and eight Low severity vulnerabilities were likewise patched in the release.

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