Hello, This seems like a conflict with other system software or an installation problem. To diagnose such conflict problems with Thunderbird, you can try one of the following: *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-including-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. If the above doesn't help you can perform a ''Clean Reinstall''. This means you remove Thunderbird's Program Files then reinstall Thunderbird. Please follow these steps: #[https://support.mozilla.org/en-US/kb/profiles-tb?esab=a&s=TB+profile&r=0&as=s#w_backing-up-a-profile Backup your current Thunderbird profile] #Download the latest version of Thunderbird from http://www.mozilla.org/en-US/thunderbird/ and save the setup file to your computer. #After the download is complete, close all Thunderbird windows (Click Exit/Quit from the menu button on the right). #Now, go ahead and reinstall Thunderbird: ##Double-click the downloaded installation file and go through the steps of the installation wizard. ##Once the wizard is finished, choose to open Thunderbird after clicking the Finish button. #At this point you can [https://support.mozilla.org/en-US/kb/profiles-tb?esab=a&s=TB+profile&r=0&as=s#w_restoring-a-profile-backup restore your backup] or setup Thunderbird accordingly <b>WARNING:</b> Do not run Thunderbird's uninstaller or use a third party remover as part of this process, because that could permanently delete your Thunderbird data, including but not limited to, extensions,emails, personal settings and saved passwords. <u>These cannot be recovered unless they have been backed up to an external device!</u> Please report back to see if this helped you! Thank you.

I haven't heard back from you, I suppose my answer was useful. If you haven't already, please mark the answer that solves the problem as such. This will help other users with similar problems find the solution more easily. Thank you for contacting Mozilla Support!

It doesn't not respond and restart nearly as much but I still have the issue. I tried both of your recommendations.

I used Thunderbird for years without problems until I installed McAffe. Since then Thunderbird has been slow, crashing and almost useless, no matter what I tried. Yesterday I returned to Norman for virus protection, and voila: Thunderbird immediately returned to normal!