First open up your new Thunderbird and select troubleshooting from the help menu. Select the show folder button in the profiles section.

Now that is the current Thunderbird profile.

Now on you old drive locate the same general location. Keeping in mins t5he actual random numbers in the folder name will differ. You will know your in the right place when the folder contains abook.mab (your address book.

Now select everything. Copy and paste to the new profile folder. Open Thunderbird and all should be good.

This is important. Copy everything, Nnt just the mail folder. Moved as a block Thunderbird will just use it, moving piecemeal requires all sorts of technical fiddling to get it right

First of all thank you for your clear directions. Sadly, it didn't work.

I have changed computers because the mother board on the previous computer is no longer functioning. The requires that I run the OLD hard drive and the NEW hard drive on the same computer.

Now, when I open up the NEW thunderbird exactly what you said occurs. I closed that version of thunderbird and specifically located the "other" copy of Thunderbird on the OLD computer. Opening and executing the same directions, it opened exactly the same folder, NOT the "old" profile folder.

As I previously stated, I cannot find the "old" profile folder on the original hard drive. Could it be when I attempted Migrating, it moved that to the "new" hard drive leaving the actual folders holding all the "records" of all my email accounts behind. I searched and searched the old hard drive to no avail. There are some Profile folders, but, they have to do with other software, not with Thunderbird.

So, I found the Profile folder on the NEW hard drive and the folders containing all the emails inbox and sent box etc. on the OLD hard drive..

Again, your help will be greatly appreciated. If I knew that Migration was going to be so useless for Thunderbird, I would have never used it in first place!

Hi Matt, Thanks again for your help.

I tried another strategy. I booted up from the old harddrive and within that boot up Thunderbird, within 10.7.5 works perfectly. I found the Profiles folder, with a different name. Copied everything ( over 7 gb) and then, shut down. Rebooting from my current harddrive running 10.8.5 I transfered the folder ( copying and pasting everything) into the NEW profiles folder with the new name and then restarted Thunderbird. It didn't work! The same thing occurs, a new window asking me if I want to start a new email address. I ask it to skip that and let me set up my own email address. Get to the window, there are NO email folders, NO email address nor INBOX's. Nothing. I use help go to trouble shooting and find the same folder again (show folder in finder) and it's got over 7gb of data in it, but, Thunderbird seems not to be accessing any of it. PLEASE HELP Thanks so much, Thomas

I am not a MAC person. So you may have have to work some of this out yourself

But first things first. Start by installing the profile switched.

On the toolbar then 

And type switcher in the box on the top right and press enter. when it has located the profile switcher click the install button.

You will not have, after a restart IIRC, an entry on the File menu to start with profile manager

Now as you do not appear to be copying things so one lot replaces the other in the same location (the only reason I can think of for your problem) copy your orinigal profile folder it will have a name with 8 random characters followed by default most likely. to you new computer.

Now use that new entry on the file menu to restart Thunderbird with the profile manager. In the profile manager select New (yes I mean new) Point the new profile to your old profile those 8 random characters.default Rename the profile as you will not have two defaults. That can only be confusing in the future..

Now continue to Thunderbird and you should be using your old profile.

Please, there has to be a way to make this work. I would appreciate it if you would understand that I HAVE FOLLOWED YOUR INSTRUCTIONS EXACTLY. I have copied the ENTIRE folder from the OLD harddrive to the NEW harddrive. I selected all from that folder and copied it into the NEW folder with a different RANDOM name. NO matter, none of the mail boxes appeared in this version of Thunderbird 38.1.0.

I also followed your most recent instructions. And, did what you said, changing profies and now it opens the ORIGINAL folder, with the FIRST random name..and STILL nothing works. Also, when I restarted thunderbird all the add-ons disappeared. Even the Profile Switcher disappeared. Clearly you are helping me as much as you can. Could you possibly help advise me as to whom else i might contact? Is there no other Thunderbird saavy person I can find who does have a Mac, who is running 10.8.5? who has migrated from 10.7.5? Thanks so much for all you help. I"m sorry it hasn't helped, but, again, I have followed your instructions perfectly. Again, thanks so much for your time. Thomas