Mozilla » Firefox Esr : Security Vulnerabilities, CVEs, Published In September 2019 (XSS)

Some HTML elements, such as &lt;title&gt; and &lt;textarea&gt;, can contain literal angle brackets without treating them as markup. It is possible to pass a literal closing tag to .innerHTML on these elements, and subsequent content after that will be parsed as if it were outside the tag. This can lead to XSS if a site does not filter user input as strictly for these elements as it does for other elements. This vulnerability affects Firefox < 69, Thunderbird < 68.1, Thunderbird < 60.9, Firefox ESR < 60.9, and Firefox ESR < 68.1.