Your TBird profile not only contains all your preferences and extensions but your e-mail folders and messages as well. Moving your profile is not that difficult. One thing to keep in mind though is your TBird profile can get quite large depending on the size of the e-mail messages you have saved so you will need to copy it to a CD/DVD or Flash Drive.

Step 1: Locate Your Profile Folder:

• On Windows Vista/XP/2000, the path is usually %AppData%\Thunderbird\Profiles\xxxxxxxx.default\, where xxxxxxxx is a random string of 8 characters. Just browse to C:\Documents and Settings\[User Name]\Application Data\Thunderbird\Profiles\ on Windows XP/2000 or C:\users\[User Name]\AppData\Roaming\Thunderbird\Profiles\ on Windows Vista, and the rest should be obvious.
• On Windows 95/98/Me, the path is usually C:\WINDOWS\Application Data\Mozilla\Thunderbird\Profiles\xxxxxxxx.default\
• On Linux, the path is usually ~/.thunderbird/xxxxxxxx.default/
• On Mac OS X, the path is usually ~/Library/Thunderbird/Profiles/xxxxxxxx.default/

NOTE: %AppData% is a shorthand for the Application Data path on Windows 2000/XP/Vista. To use it, click Start > Run… (use the search box on Vista), enter %AppData% and press Enter. You will be taken to the “real” folder, which is normally C:\Documents and Settings\[User Name]\Application Data on Windows XP/2000, C:\users\[User Name]\AppData\Roaming on Windows Vista.

Step 2: Make note of the name (the random string of 8 characters) of your profile folder, you will need this later.

Step 3: Copy The Contents. Once you see your profile folder (xxxxxxxx.default) just select and copy it, this will copy all the files and folders within it. Again, depending on the size and number of e-mail messages you have, the profile folder can be quite large and this process may take a little time.

Step 4: Paste The Contents. On the new machine locate the top-level profile folder (on Windows this would be the folder called Profiles) and paste your profile folder xxxxxxxx.default) here.

Step 5: Start and then exit Thunderbird. IMPORTANT: this starts Thunderbird with a FRESH profile so that it will create a profiles.ini file.

Step 6: Edit profiles.ini . From the path in Step 1, go to the folder called Thunderbird. There you will find a file called profiles.ini . Open the file using Notepad or any other text editor. The last line should read something like this: Path=Profiles/54a7fhol.default Enter the random string of 8 characters from Step 2 between the ‘/’ and ‘.default’ . Save the file and exit the editor.

Step 7: Restart Thunderbird. This time when you start Thunderbird your profile will load and you will have all your add-ons and e-mail messages.

Source: Thunderbird How To Manage Profiles