How to Open/Import MBOX File in Mozilla Thunderbird?

Steps to Open/Import MBOX File in Thunderbird:

Step 1: Open Mozilla Thunderbird.
Mozilla Thunderbird

Step 2: Go to Setting » Add-ons
Add-ons Option

Step 3: Click on Extensions. Search Import Export Tool.
Thunderbird Extensions

Step 4: In Add-ons Windows, check ImportExportTools and click on "Add to Thunderbird".
After this, you will get a dialog box with the installation option of ImportExportTools.
Thunderbird Add-ons Window

Step 5: Click on "Install Now" button to start the installation process.
Add-ons Installation

Step 6: Restart the Mozilla Thunderbird. Click on "Local Folders" to import MBOX file there.
Import MBOX File

Step 7: Go to Setting » Tools » ImportExportTools » Import MBOX File.
Thunderbird Add-ons Option

Step 8: With "Import directly one or more mbox files" option selected, click Ok.
Option to Import MBOX File

Step 9: Select MBOX file and click on "Open" button.
Open MBOX File

Step 10: Your MBOX file will instantly appear in Local Folders. Just click on MBOX file and view in preview pane.
View MBOX File

These are the simple steps to import MBOX file in Mozilla Thunderbird. If you have still any doubt or question, feel free to ask.