Upgrading Version 2 Thunderbird to Version 3
Introduction
If you have updated recently your version of Linux Distro in Ubuntu, Mint and others you might have hit on a couple of upgrade problems associated with the Thunderbird Version released with the distro. This howto covers the instructions needed to overcome these problems. At least one of the fixes is very simple the other is only slightly more complex.Thunderbird Problem
When upgrading from one version to the next especially distro's one does not want to type in again such things as address books and profile details for any give email account. No the smart Linux user saves a copy of the hidden dot file which retains all the mail passwords and connection details, well everything really. But here is the thing Thunderbird Ver 3 does not see this hidden file for Version 2 even if you put it back in your home directory, the reason it does not see this is because Thunderbird Version 3 uses a different hidden dot file to that of Version 2. Before Ver 3 the procedure was to copy the contents of the previous version and put in the new copy of the hidden dot file.Thunderbird Fix
Thunderbird Ver 2 hidden directory is identified by .mozilla-thunderbird this was also true of previous versions this sits in your home directory so given the importance of emails and the data that it often contains this is a folder you should backup regularly. Thunderbird Ver 3 hidden directory is just as important to backup after you have migrated it and resides in the same home directory as that of Version 2 the hidden dot file in this case is identified by .thunderbird. So in order to upgrade from Thunderbird version 2 to version 3 all you do is copy the hidden dot file for version 2 to a usb stick with sufficient capacity and paste this back into your own home directory. You paste this dot folder after you have upgraded your distro but before you started the new version of Thunderbird. you then rename the the folder to what Thunderbird now expects thus.If you have previously started Thunderbird Version 3 then run the above command your system will tell you that the folder already exists, if this is the case rename the dot thunderbird folder rather than delete it, just in case, you can always delete the folder once the migration has been successful. Now start Thunderbird migration should have been successful and all your data, emails, address book and connections settings should be functioning perfectly.

