Comment 57 for bug 885525

(In reply to ncnmra from comment #53)
> I'm not sure how this influences Shift-Delete behavior since I don't usually use it.

"Shift+Delete" is "Delete without copy to trash when move to trash model" in Tb. This is similar to MS Window's Shift+Delete of file/directory.
When IMAP, "delete a mail"=="store +Flag (\Deleted)".
Difference from perspective of IMAP is;
  "Move to trash" model :
     Delete : "uid xxx copy trash" + "uid xxx store +Flag \Deleted"
     Shift+Delete : "uid xxx store +Flag \Deleted"
  "Just mark it as deleted" / "Remove immediately" :
     Delete / Shift+Delete : "uid xxx store +Flag \Deleted"
i.e. "Shift+Delete" is never influenced by "unsubscribe [Gmail]/Trash".

> Workaround #1 seems to work for now with the exception that I cannot access the [Gmail]\Trash folder from TB.

If you want to copy/move mail to [Gmail]/Trash, subscribe it again.
  subscribe [Gmail]/Trash, collapse/expand account if required,
  copy/move mails to [Gmail]/Trash or delete mails while trash==[Gmail]/Trash,
  unsubscribe [Gmail]/Trash again.
As far as auto-expunge of Gmail is enabled, any Gmail Label is removed from mail and mail flagged as \Deleted is automatically removed(expunged) from IMAP folder(s) by Gmail, and mail is removed from [Gmail]/All Mail too by Gmail, and the mail will be permanently erased at [Gmail]/Trash after 30 days.

Another solution of issue of "you can't acces [Gmail]/Trash if unsubscribed".
  Use "Just mark it as deleted" or "Remove immediately".
I think "adding Gmail Label of [Imap]/Trash or Something/Trash by move to trash model and deleting mail in Tb" is convenient, but I don't think it's mandatory for any Gmail IMAP & Thunderbird user.