More of a comment than a question as I have finally succeeded in what I was trying to do. The instructions that have been posted on this forum about how to transfer email accounts from an old macbook to a new Macbook are wrong - it is the whole Thunderbird folder in Library that needs to be copied, not the Profile folder as stated. There was a lot of misleading comments on the forum and it took a long time of sifting through trying to find the solution. So - here is my method. 1 - Install Thunderbird on new Mac. Open it, but don't set up an account. Then quit Thunderbird. 2. On old computer - in finder, press "option" and select "library" from the "Go" menu. Scroll down to Thunderbird folder and copy the whole folder onto a flash drive. 3. On new computer - in finder, press "option" and select "library" from the "Go" menu. Scroll down to Thunderbird folder and delete the entire folder by dragging to trash. 4. Insert flash drive to new computer, then copy the Thunderbird folder into the location from which you deleted the folder. 5. Re-open Thunderbird and all your emails should be there.

I hope this helps someone else - it would have saved me two days of headaches!