You will see vivid-security/main (or just differs in release name in another version of Ubuntu) when installing.You should check what version number available for your Ubuntu system after doing the reloading.Mozilla has decided to speed up the release cycle of Thunderbird and Firefox.This is all good except that it often breaks Add-ons.Some applications make Simple MAPI calls to check for new messages.This will start the default email client, if its not already running.
You can prevent this by configuring Thunderbird not to be the default mail client. Is the entry slightly indented, underneath (Windows Explorer) or does it have a different parent? Right click on the Thunderbird entry and select properties 6. That will tell you the command line used to launch it.
Alternatively, open the "Session and Startup" from the settings manager and uncheck the "Automatically save session on logout" option. Try closing thunderbird and anything else you don't want starting.
Settings Manager - Session and Startup - Session tab Clear saved sessions - Save Session I get odd things starting from time to time and that appears to deal with it here.
If you can identify what software is checking for new mail on startup you could also try disabling that feature. Normally it looks something like "C:\Program Files\Thunderbird\thunderbird.exe" 7.
Google's Picasa software, some BIOS's, a helper application associated with the IBM Rapid Access III Keyboard, and a Active Desktop theme for a IBM Thinkpad have been known to do this. To the left of the Verify button it has a field that identifies that parent process, and its process id (PID).