Mozilla Thunderbird is a standalone mail and newsgroup client. This update upgrades Thunderbird to version 91.3.0. Security Fix(es): * Mozilla: Use-after-free in HTTP2 Session object * Mozilla: Memory safety bugs fixed in Firefox 94 and Firefox ESR 91.3 * Mozilla: iframe sandbox rules did not apply to XSLT stylesheets (CVE-2021-38503) * Mozilla: Use-after-free in file picker dialog (CVE-2021-38504) * Mozilla: Firefox could be coaxed into going into fullscreen mode without notification or warning (CVE-2021-38506) * Mozilla: Opportunistic Encryption in HTTP2 could be used to bypass the Same-Origin-Policy on services hosted on other ports (CVE-2021-38507) * Mozilla: Permission Prompt could be overlaid, resulting in user confusion and potential spoofing (CVE-2021-38508) * Mozilla: Javascript alert box could have been spoofed onto an arbitrary domain (CVE-2021-38509) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.