To import your Facstaff Archive into Thunderbird, you will first need to install the Add-on, ImportExportTools.  ImportExportTools is available for download here.  Once download you will want to install the Add-on by doing the following:

    1.    Download and save the file to your hard disk.
    2.    In Mozilla Thunderbird, open Add-ons from the Tools menu.
    3.    From the options button next to the add-on search field, select "Install Add-on From File..." and locate the downloaded add-on.
    4.    Once installed, restart Thunderbird.

To import the mbox files you will want to select Local Folders, you can choose to create a sub folder to import the mbox files into or you can stay selected on Local Folders:

With the destination folder selected go to Tools>ImportExportTools>Import mbox file:

You will be asked how you want to import them select 'Import directly one or more mbox files' and click OK.

You will then be prompted to select your mbox file or files and then click Open.  Your archived messages will appear in the chosen folder.

Please contact your Local Support Provider if you have any trouble.