I was able to import the names of my contacts but the email addresses didn't appear. After working with this with all the ideas I had, I noticed that in the import questions in Thunderbird, you are asked to tick or untick various columns, like First Name, Last Name, Primary Email, Secondary Email. I noticed when I opened the address book after importing the addresses, that there isn't a Primary Email and Secondary Email, there is only Email.

I was able to overcome this problem by removing the addresses from where they were appearing (either under Last Name or as part of First Name) and pasting them into "Email". I don't know if this could have been avoided by putting more commas or tabs into the file I was trying to import, csv or txt. I also don't know if it was caused because the list of options was looking for Primary Email rather than for Email and couldn't find it. Once in the correct column, the contact list became workable, I could use autocomplete and could create new lists.