The pane only displays after you attach the first file. You can drag and drop a file where the pane will be at the end of the address fields to attach the file.

Yes I figured that out prior to posting, however why did Mozilla remove the pane? It appears to me that there was no reason to remove it. It also does not solve the problem with the missing attachments when using (Edit as new Message). I used this quite a bit. Now I have to add the attachments again. Thunderbird should add the Attachment pane as a Display Option. On or Off and load attachments when editing previous sent email. Yes or No

Thanks

How old of a version did you update from? I have never seen the pane be there all the time.

Exactly what advantage does having the pane show all the time give? It just takes up space when not needed.