Mozilla developer Jesse Ruderman demonstrated that
by tampering with the window.__proto__.__proto__
object,
one can cause the browser to place a lock on a non-native object,
leading to a crash. Although we have not demonstrated such control, a
determined attacker might be able to exploit this crash to run
arbitrary code on a victim's computer.
Thunderbird shares the browser engine with Firefox and could be vulnerable if JavaScript were to be enabled in mail. This is not the default setting and we strongly discourage users from running JavaScript in mail.
Disable JavaScript until a version containing these fixes can be installed.