Start *Windows'* safe mode with networking enabled - win7 http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 Still In Windows safe mode, start thunderbird in safe mode - http://support.mozillamessaging.com/en-US/kb/safe-mode

Does problem go away?

- If no, then cause is either: bug in Thunderbird, in your Thunderbird profile, or your mail provider. Please post into topic the contents of Help | Troubleshooting | copy text to clipboard

- If yes, (still in Windows safe mode) ... start Thunderbird normally

   -- If problem is still gone, then cause is a program loaded during windows startup.  Possibilities include: antivirus SW, virus/malware, background downloads such as program updates
   -- If problem is came back, then cause is likely a Thunderbird addon - eliminate them by disabling each one at a time in Tools | addons | extensions and restarting

Thunderbird always works for a while after a reboot, so safe mode doesn't tell us much here. I'm in Safe Mode now, and Thunderbird has not frozen up yet.

So...How can I find out what is freezing Thunderbird? Or, if we go out on a limb, and say it's "working" in Windows Safe Mode, what are the next steps to finding what is breaking Thunderbird?

Mozzilav said

Thunderbird always works for a while after a reboot, so safe mode doesn't tell us much here. I'm in Safe Mode now, and Thunderbird has not frozen up yet.

And if that continues to work well, what it means is something that is loaded during Windows' startup is interfering with Thunderbird. Typically antivirus or firewall software. But could be something else.

You can look up your AV software at https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues to see if something has already been previously reported.

Let us know what you find

The major problem is, once it goes into "Not responding" mode, killing the process and reopening freezes back up withing seconds, every time.

Is there any way to detect the culprit while it's happening? If I can kill some other process to bring back Thunderbird without having to reboot, it would help for now. But it is currently in an unusable state.

P.S. I have unchecked "Allow anti-virus clients to quarantine individual incoming messages", as outlined here: https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues#AVAST It appears it did NOT actually solve the user's issue, but we'll see how it goes...

Well, unchecking "Allow anti-virus clients to quarantine individual incoming messages" did not work :( Crashed again.

re : OK in Windows safe mode Do you have AVAST scanning Thunderbird program and/or thunderbird profile folders ? Do you have AVAST scanning incoming mail ?

Suggest you stop AVAST from checking anything to do with Thunderbird. How to make exclusions from the File System Shield

• https://www.avast.com/faq.php?article=AVKB168

Are you using hardware acceleration ? 'tools' > 'Options' > Advanced' > 'General' tab uncheck: Use hardware acceleration when available' clickon OK

- Hardware acceleration has always been unchecked. - Thunderbird crashes even with Avast disabled.

This is such a consistent crash, there should be a way to diagnose, right?

It is so borked that I am sadly looking at Thunderbird alternatives.

P.S. Not sure if this is an inappropriate place, but if anybody knows a good Thunderbird alternative (not Outlook), please recommend.

Another possibility, is delete the Thunderbird program directory (NOT your profile data), and reinstall from https://www.mozilla.org/en-US/thunderbird/ --- one of the several ideas you can try at https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems

Let us know what works?

This is almost certainly caused by Avast - so noted in topic title. However, reporter seems to be skipping this idea.

Just updated to TB 38.5.0 and Avast is now 11.1.2245. We'll see if the crashes go away.

Thanks.

I would suggest you create an exception in the Avast program for our Thunderbird profile folder and it's sub folders and see if that helps. I think it will.

How are you going getting support from Avast for their product causing crashes in Thunderbird?

Thunderbird has been relatively stable in the past few weeks. Perhaps updates to TB and/or Avast have resolved the freezing issues. Thank you for all the thoughtful troubleshooting.

I had this problem also and solved it (3 days and counting) after reading some of the links above.

Avast has a mail shield which can be turned off, temporarily for testing and permanently if this is your cause. It can be found under Settings>Active protection>Mail Shield. Slide to off and select the timeframe.

Seems like you are still protected by Avast File Shield and reasonable mail behavior. I assume mail and password are still protected by SSL/TSL if your mail server supports this. Obviously, the encryption problem has to fixed.