Security update for MozillaThunderbird

This update for MozillaThunderbird fixes the following issues: - Mozilla Thunderbird 78.8 * fixed: Importing an address book from a CSV file always reported an error * fixed: Security information for S/MIME messages was not displayed correctly prior to a draft being saved * fixed: Calendar: FileLink UI fixes for Caldav calendars * fixed: Recurring tasks were always marked incomplete; unable to use filters * fixed: Various UI widgets not working * fixed: Dark theme improvements * fixed: Extension manager was missing link to addon support web page * fixed: Various security fixes MFSA 2021-09 (bsc#1182614) * 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 This update was imported from the SUSE:SLE-15-SP2:Update update project.