User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:65.0) Gecko/20100101 Firefox/65.0

Steps to reproduce:

I am using Windows 10 x64 Pro.
32bit Thunderbird 60.5.2

I use my scanning software to scan a document to sent via email.
I scan the document.
I indicate that I am done scanning the document.
(Creating a multi-page pdf with scanned document as the contents)

Actual results:

I get a "Confirm" popup window.
The message is: Another application is attempting to send mail using your user profile. Are you sure you want to send mail?
There is a check box: Warn mo whenever other applications try to send mail from me.
There are 2 buttons: OK (default), Cancel
The 'x' is enabled.

After clicking on any of the buttons or 'x' the window goes away.

Expected results:

There are 2 things wrong:

1. The buttons should be 'Yes"(default) and "No", not OK and Cancel.

2. The send message dialog should appear populated with the pdf attached as an attachment.

The expected should perhaps be worded:

I get a "Confirm" popup window.
The message is: Another application is attempting to send mail using your user profile. Are you sure you want to send mail?
There is a check box: Warn me whenever other applications try to send mail from me.
There are 2 buttons: Yes (default), No
I select yes and the send message dialog should appear populated with the pdf attached as an attachment.

Whatever ControlCenter4 is,

ControlCenter4 is software that gives you quick and easy access to many functions such as Scan, Photo Print and PC-FAX of your Brother printer/scanner.

See bug 1530820 comment #30.