Try a clean installation instead, as follows: # Uninstall ALL versions of Thunderbird via Control Panel and reboot. # Delete the '''Mozilla Thunderbird''' folder from the following locations: #*C:\Program Files #*C:\Program Files (x86) # Download a new copy from thunderbird.net and install it. This will not affect your profile (messages, addresses, settings etc). Also See [[Profiles - Where Thunderbird stores your messages and other user data]]