That sounds more like an antivirus issue than a Thunderbird one. Looking at the crash report it would appear the thread that is crashing has two libraries in use. One distributed by Microsoft as part of their development environment and another that is a part of own cloud that I think from what I just read shows the syncing icons when things sync. https://crash-stats.mozilla.org/report/index/6c97ce14-2f2f-4f09-9424-6c7780240608 Perhaps try reinstalling Thunderbird and owncloud, or uninstalling the owncloud and see if things change. You might also want to try; Does Thunderbird work as expected with your OS started in '''[http://en.wikipedia.org/wiki/Safe_mode safe mode with Networking]'''. Instructions for each operating system: [https://support.microsoft.com/en-us/windows/start-your-pc-in-safe-mode-in-windows-92c27cff-db89-8644-1ce4-b3e5e56fe234 Windows 10/11], [https://support.microsoft.com/en-us/windows/windows-startup-settings-including-safe-mode-7f31dcea-6427-0ba0-ec1b-729a56321cd3 Windows 8], [https://support.microsoft.com/en-us/windows/advanced-startup-options-including-safe-mode-b90e7808-80b5-a291-d4b8-1a1af602b617#start-computer-safe-mode=windows-7 Windows 7], [http://support.apple.com/kb/ht1564 OSX]

I did an update to Owncloud a couple of days ago so I'm pretty sure that's the cause thank you. Travelling at the moment but will investigate further ASAP.