Multiple critical security vulnerabilities affecting Mozilla Firefox and Thunderbird were fixed in versions Firefox 159, Firefox ESR 153.6, Thunderbird 159, and Thunderbird 153.6. These include same-origin policy bypasses, sandbox escapes, privilege escalations, information disclosures, and numerous use-after-free issues across various components such as DOM, JavaScript engine, graphics, networking, layout, audio/video, and storage. The vulnerabilities have a high CVSS score of 9.8, indicating severe impact on confidentiality, integrity, and availability.