For anybody in the future... this is one reason why I have stayed with Thunderbird since it began... Going from the Windows re-installs to Windows re-installs to finally from the Windows platfom to the Mac platform, and then from OS X fresh installs from one computer to the next to the next...
The only hiccup was when I tried Postbox for a few months.
You can take your Thunderbird profile and simply copy the contents of it to the new profile directory that has automatically been created on the new platform:
In order, open Thunderbird on your new platform. This creates a new user profile directory. You must take the files from the old platform and copy them to this folder, AFTER you have quit Thunderbird on the new platform. After the profile data has been copied, simply launch Thunderbird on the new platform and all your email settings and mail should be there, ready for you to resume where you left off...