The updated thunderbird packages fix security issues:
Covert Content Attack on S/MIME encryption using a crafted multipart/ alternative message. (CVE-2019-11739)
Memory safety bugs fixed in Firefox 69, Firefox ESR 68.1, Firefox ESR 60.9, Thunderbird 68.1, and Thunderbird 60.9. (CVE-2019-11740)
Same-origin policy violation with SVG filters and canvas to steal cross-origin images. (CVE-2019-11742)
Cross-origin access to unload event attributes. (CVE-2019-11743)
XSS by breaking out of title and textarea elements using innerHTML. (CVE-2019-11744)
Use-after-free while manipulating video. (CVE-2019-11746)
Use-after-free while extracting a key value in IndexedDB. (CVE-2019-11752)