Thunderbird has a somewhat hidden 'Saved Files/Download ' tab, which you can access via Tools menu or Ctrl J.
I think it is a very useful feature - especially in the context of Thunderbird as a desktop application.
It would be useful if this tab was always open, or you could add a shortcut button (I could not find one)
Also, in the file listing interface, perhaps the location of the files and the 'open containing folder' shortcut were made more prominent. (There is a lot of horizontal space available)
(the problem - perhaps you save an attachment, then cannot remember which folder tree it was put in)
Perhaps saved attachments can be linked- to from their original message too. (imagine this is more tricky to achieve)