Okay, this is what I did to get Thunderbird to work.
First up - Locate the thunderbird directory
Second, View > Show Hidden Files.
Now locate the .thunderbird folder. At this point, it might be a good idea to make a copy (backup) of the .thunderbid folder somewhere safe.
Carefully delete the thunderbird folder (and make sure you are deleting the correct thunderbird folder - NOT THE _._thunderbird folder)
To be safe, I renamed the .thunderbird folder .thunderbird.old - and I would advise you to do the same - even though you made a backup copy, right?
Download the latest version of Thunderbird from Mozilla's site and put it in your home folder (whatever that is called)
Double click on the compressed file to extract it and allow it to extract into the home folder.
At this point, you can now start Thunderbird as you usually do - *But wait, there's more.*
You will be prompted to create a new account and I think you need to complete this. To be honest with you, I didn't try canceling the process, you might be able to, I'm not sure. If someone else tries this please post your results here for the benefit of everyone else.
What I did, at this point was to now locate both the .thunderbird folder that was recently created by Thunderbird when you just started it up and the old .thunderbird folder.
Open both folders up on your desktop so that you can see both of them. Open up the cryptically named profile folders and you should see the your Mail folder. Now open up the Mail folder in both windows.
Copy the entire contents of the mail folder from your old profile Mail folder into your new profile Mail folder. WARNING - DO NOT MAKE THE MISTAKE OF COPYING THE NEW MAIL FOLDER INTO YOUR OLD MAIL FOLDER - but if you do, you made a backup, right.
Once the operation is complete you can restart Thunderbird and enjoy all the sweet functionality that a correctly operating Email/RSS/Calendar brings you, assuming you use Thunderbird for all of those things.