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. This vulnerability affects Firefox ESR < 91.9.1, Firefox < 100.0.2, Firefox for Android < 100.3.0, and Thunderbird < 91.9.1.
CWE-1321, CWE-1321