NPAPI plugins, such as Adobe Flash, can send non-simple cross-origin requests, bypassing CORS by making a same-origin POST that does a 307 redirect to the target site. This allows for a malicious site to engage in cross-site request forgery (CSRF) attacks. This vulnerability affects Thunderbird < 60, Thunderbird < 52.9, Firefox ESR < 60.1, Firefox ESR < 52.9, and Firefox < 61.