How to open a Thunderbird Address Book File

What for?

Just to explore the file.....

Address books are sqlite files. So you'll need a sqlite viewer. I'm certain you'll find something when you search for it.

Something like this?

https://sqlitebrowser.org/

Exactly.

What file type am I looking for? As when I open the program and import the file it doesn't see the file?

Maybe, if you explain exactly what your objective is, we can help better.

I basically lost an email contact and its on my last back up folder in which I need to look up in order to retrieve it.

In that case, you might create a new addressbook, and use the import feature to import the backed up addressbook. Then, you can view and copy the lost email address.

Importing that backup from that address book.

1.Open Thunderbird and click on the Address Book icon.

2.Click the Import button and select Address Books.

3.Follow the on-screen prompts to select and upload your backup file (.csv format).

4.Once imported, your contacts will appear as a new address book. You can now browse or search it to find and copy the information you need.