Problem
You are trying to start Thunderbird, but it then says it is already running, even though you never had it open.
Cause
This is a known issue that happens when Thunderbird did not close properly.
This often leaves a 'lock' file the application sees and believes it is still running or running in the background somewhere.
This can also happen on Linux systems if a user is logged onto another machine using Thunderbird and then trying to use another linux machine with their networked home directory.
http://kb.mozillazine.org/Profile_in_use
For reference in thunderbird Profile Folder...
Solution
You will want to go into the Profile Folder on your machine...
For Linux
The profile folder is located at ~/.thunderbird/<randomcharacters>.default
For Mac OSX
The profile folder is located at ~/Library/Thunderbird/Profiles/<randomcharacters>.default
For Windows
The profile folder is located at C:\Users\<Windows user name>\AppData\Roaming\Thunderbird\Profiles\<randomcharacters>.default
Remove the lock files...
Remove the following files if they are there:
.parentlock
parentlock
lock
parent.lock
NOTE
For Mac and Linux/Unix users... the '.parentlock' is considered a 'hidden' file. In order to see it, you will need to use the command 'ls -la' to see hiddent files and folders.
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