Log Message:
thunderbird: Update to 78.6.0

* Fix build with devel/cbindgen-0.16.0.

Changelog:
New
MailExtensions: Added browser.windows.openDefaultBrowser()

Changes
Thunderbird now only shows quota exceeded indications on the main window
MailExtensions: menus API enabled in messages being composed
MailExtensions: Honor allowScriptsToClose argument in windows.create API
function
MailExtensions: APIs that returned an accountId will reflect the account the
message belongs to, not what is stored in message headers

Fixes
Keyboard shortcut for toggling message "read" status not shown in menus
OpenPGP: After importing a secret key, Key Manager displayed properties of the
wrong key
OpenPGP: Inline PGP parsing improvements
OpenPGP: Discovering keys online via Key Manager sometimes failed on Linux
OpenPGP: Encrypted attachment "Decrypt and Open/Save As" did not work
OpenPGP: Importing keys failed on macOS
OpenPGP: Verification of clear signed UTF-8 text failed
Address book: Some columns incorrectly displayed no data
Address book: The address book view did not update after changing the name
format in the menu
Calendar: Could not import an ICS file into a CalDAV calendar
Calendar: Two "Home" calendars were visible on a new profile
Calendar: Dark theme was incomplete on Linux
Dark theme did not apply to new mail notification popups
Folder icon, message list, and contact side bar visual improvements
MailExtensions: HTTP refresh in browser content tabs did not work
MailExtensions: messageDisplayScripts failed to run in main window
Various security fixes

Security fixes:
#CVE-2020-16042: Operations on a BigInt could have caused uninitialized memory \ 
to be exposed
#CVE-2020-26971: Heap buffer overflow in WebGL
#CVE-2020-26973: CSS Sanitizer performed incorrect sanitization
#CVE-2020-26974: Incorrect cast of StyleGenericFlexBasis resulted in a heap \ 
use-after-free
#CVE-2020-26978: Internal network hosts could have been probed by a malicious webpage
#CVE-2020-35111: The proxy.onRequest API did not catch view-source URLs
#CVE-2020-35112: Opening an extension-less download may have inadvertently \ 
launched an executable instead
#CVE-2020-35113: Memory safety bugs fixed in Thunderbird 78.6