Security researcher Cody Crews reported a method to call a content level constructor that allows for this constructor to have chrome privileged accesss. This affects chrome object wrappers (COW) and allows for write actions on objects when only read actions should be allowed. This can lead to cross-site scripting (XSS) attacks.
In general these flaws cannot be exploited through email in the Thunderbird product because scripting is disabled, but are potentially a risk in browser or browser-like contexts.
Vulmon