Log Message:
thunderbird: Update to 78.8.0

Changelog:
Fixes
Importing an address book from a CSV file always reported an error

Security information for S/MIME messages was not displayed correctly prior to a
draft being saved

Calendar: FileLink UI fixes for Caldav calendars

Recurring tasks were always marked incomplete; unable to use filters

Various UI widgets not working

Dark theme improvements

Extension manager was missing link to addon support web page

Various security fixes

Security fixes:
#CVE-2021-23969: Content Security Policy violation report could have contained
the destination of a redirect
#CVE-2021-23968: Content Security Policy violation report could have contained
the destination of a redirect
#CVE-2021-23973: MediaError message property could have leaked information
about cross-origin resources
#CVE-2021-23978: Memory safety bugs fixed in Thunderbird 78.8