Security Vulnerabilities fixed in Firefox 100.0.2, Firefox for Android 100.3.0, Firefox ESR 91.9.1, Thunderbird 91.9.1 — Mozilla

If an attacker was able to corrupt the methods of an Array object in JavaScript via prototype pollution, they could have achieved execution of attacker-controlled JavaScript code in a privileged context.
An attacker could have sent a message to the parent process where the contents were used to double-index into a JavaScript object, leading to prototype pollution and ultimately attacker-controlled JavaScript executing in the privileged parent process.