The only thing I can think of is that my VPN client connection may have gone down after the update at which point I connected to a different VPN server so maybe something internal to Thunderbird got in some weird state? Not sure but I've since rebooted several times and still have the same behavior "Killed: 9."

I've tried looking for any log files but I have no idea where any Thunderbird logs are kept. I see a folder called ~/Library/Thunderbird/Crash\ Reports that contains several ASCII files named "InstallTime[Apparent time stamp format] but even when I examine the most recent one that was created today on or around the time I performed the update to 78.5.1, it contains no crash data (to my eyes), just some 10-digit number.

I'm puzzled. Please help.

Thanks.

OK, after digging a little more I found some crash info at the system level by invoking the /Applications/Utilities/Console program in osx, look at the Crash Reports tab and I do see crashes for every time I have tried to unsuccessfully launch Thunderbird after the update to 78.5.1. They all have similar forms:

" Process: ReportCrash [1041] Path: /System/Library/CoreServices/ReportCrash Identifier: ReportCrash Version: 15016 Code Type: X86-64 (Native) Parent Process:  ??? [1] Responsible: ReportCrash [1041] User ID: xxx

Date/Time: 2020-12-02 15:31:42.376 -0800 OS Version: Mac OS X 10.15.7 (19H15) Report Version: 12 Bridge OS Version: 3.0 (14Y908) Anonymous UUID: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

Time Awake Since Boot: 1800 seconds

System Integrity Protection: enabled

Crashed Thread: 6

Exception Type: EXC_CRASH (Code Signature Invalid) Exception Codes: 0x0000000000000001, 0x0000000000000000 Exception Note: EXC_CORPSE_NOTIFY

Termination Reason: Namespace CODESIGNING, Code 0x2

kernel messages: ...

Application Specific Information: dyld3 mode Analyzing process: thunderbird[1092], path: /Applications/Thunderbird.app/Contents/MacOS/thunderbird; parent process: [1], path: /sbin/launchd

...

Thread 6 Crashed: 0 com.apple.CoreSymbolication 0x00007fff511a8a15 thread_exit_due_to_bad_access() + 0 1 com.apple.CoreSymbolication 0x00007fff511a4672 ScanInstructionsForMissingSecondFrameLocation_Intel(_CSTypeRef, bool, unsigned long long, unsigned char const*, unsigned long long, unsigned long long, unsigned long long*, unsigned long long*, _CSTypeRef, mapped_memory_t*) + 46 2 com.apple.CoreSymbolication 0x00007fff5113ae90 CheckForSecondFrame2(sampling_context_t*, CSThread&) + 327 3 com.apple.CoreSymbolication 0x00007fff511a4de7 invocation function for block in CheckForSecondFrame(sampling_context_t*, CSThread&) + 30 4 com.apple.CoreSymbolication 0x00007fff51134930 CSCppExceptionSafeThread::sacrificial_thread_init() + 80 5 com.apple.CoreSymbolication 0x00007fff511348dc thread_init_trampoline(CSCppExceptionSafeThread*) + 9 6 libsystem_pthread.dylib 0x00007fff71abe109 _pthread_start + 148 7 libsystem_pthread.dylib 0x00007fff71ab9b8b thread_start + 15

Thread 6 crashed with X86 Thread State (64-bit):

 rax: 0x0000000000000000  rbx: 0x0000000000000003  rcx: 0x0000000000000000  rdx: 0x0000000000000001
 rdi: 0x0000000000000002  rsi: 0x0000700007cd2ad0  rbp: 0x0000700007cd2a60  rsp: 0x0000700007cd2a18
  r8: 0x0000700007cd2b20   r9: 0x0000000000000003  r10: 0x0000700007cd2ad0  r11: 0x00007fbdc3616e40
 r12: 0x0000000000000002  r13: 0x000000011b29410b  r14: 0x0000000000000001  r15: 0x0000000000000000
 rip: 0x00007fff511a8a15  rfl: 0x0000000000000202  cr2: 0x000000011b29410b
 

Logical CPU: 2 Error Code: 0x00000004 (no mapping for user data read) Trap Number: 14

... "

Not sure what's going on but maybe a problem with OSX Code Signature / Code Signing?

I got the same problem since the update this morning. I am on the MacOS 11.0.1 (latest BigSur version).

Not sure how we as users can solve this. Looks like developers need to tell us how (if even possible) to work around this?

Hello, any developers out there?

In my case Thunderbird started working again after some time. I did nothing so I don't know what the problem solved.

OK, I got it working. But only *after* I completely un-installed Thunderbird by right-clicking on it in the Applications folder, selecting "Move to Trash", downloading the latest OSX-specific .dmg application bundle from the thunderbird.net website (with no apparent SHA sum or MD5 sum, which means, how do we as consumers know if this is a legit binary or not?), and re-installing at which point the familiar OSX popup occurs, asking if I want to open the Thunderbird app downloaded from the internet, to which I click the Open button and now, Thunderbird is working for me once again (verified after a couple of reboots).

This still looks like a serious bug to me and whoever is responsible for developing/porting to OSX needs to look into this. I might file a bugzilla bug if I have time.