Hello there We have read your message. We try to help you. try to Start Thunderbird in safe mode. http://kb.mozillazine.org/Safe_mode That is how you indentify your problem with software for Thunderbird use. go to the add- onn manager or extensions search and look for an extension named Xul Runner or everything that looks like it. If there is some extension add- on remove it and try to restart thunderbird again Or reinstall Thunderbird after '''deleting''' every profile of the software from Thunderbird. A fresh install. '''C:\Program Files\Mozilla Thunderbird\ '''C:\Program Files (x86)\Mozilla Thunderbird\'''''' Try to use 64-bits Software? 32-bits is possible oke. Greetings Firefox volunteer.