Some questions.

Were the folders of mail under local folder or somewhere else? Has Thunderbird been set up on the new machine? It is far easier to migrate a whole profile than bits. But after the new profile gets a load of mail that will be lost in the update then it is back t trying to move bits.

Yes they where under Local Folders. Set up Thunderbird right after Firefox, couldn't read anything about how to look for old files. Please let me know what you think. Bob

First things first. I am not a mac person.

However first locate your data files in the old profile folder. this should help. https://support.mozilla.org/en-US/kb/profiles-tb#w_where-is-my-profile-stored Note that the ~library location may well be hidden by OSX. Once you locate it, diginto the mail folder and the "local folders" folder You should see a file with the same name as those missing folders, accompanied by an MSF file. That file is the mail.

Now in your new install. Go to the troubleshooting information on the help menu. Click the show profile button close Thunderbird. Now go the exactly the same location in the new profile in finder as you were in the old. Copy the files one profile to the other

Now go up to the profile folder in both cases. Locate the abook.mab and history.mab files in the old profile and replace those in the new profile with those from the old.

Open Thunderbird. With luck and you putting everything in the right place both the personal address book, the collected address book and the folders should be back.

Were there more address books? (the mac address book being something we have no control over)

Matt-My old Macbook Pro would not start up. I had Geek Squad try to transfer all the data they could to the new iMac. No Thunderbird info showed. I am going to go back there with my old drive that they removed and see if they can search it like its says in your response 'how to locate old profiles' If you think of anything else, please let me know. Thanks Bob Leat