We generally advise those who insist on using CCleaner to set it to leave Thunderbird's profile alone. Thunderbird uses .json files which CCleaner inappropriately identifies as dangerous. Thunderbird uses them to store layout, configuration etc. Given that we tell people not to use CCleaner, we don't have much experience in the exercise of continually running it.

Zenos - Since I've found that CCleaner can be used to reset TBird, that's what I've been using. What I'm looking for is the '''''reason''''' that TBird locks up and then what I can do to fix it.

I suggest you try the two standard diagnostic approaches below , and leave CCleaner out of it. If all else fails you can press Alt+Ctrl+Delete and select to run the task manager. It offers that ability to close non responsive programs. it also allows you to look as the CPU consumption of programs, often freezing relates to Thunderbird and another program using loads of CU cycles. *Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender. *Restart the operating system in '''[http://en.wikipedia.org/wiki/Safe_mode safe mode with Networking]'''. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: [http://windows.microsoft.com/en-us/windows-8/windows-startup-settings-safe-mode Windows 8], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 Windows 7], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-vista Windows Vista], [http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx?mfr=true" Windows XP], [http://support.apple.com/kb/ht1564 OSX] ; If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.