Recently, developers decided it was a neat idea to make all default folders have the same naming convention. This has caused a lot of confusion and many people now find their imap account folders do not have same name as displayed on server. This has meant the 'All Mail' folder got incorrectly renamed as 'Archives' and you may find the 'Sent Mail' folder has also been renamed as 'Sent'. You may also discover the 'Trash' or 'Bin' has been renamed as 'Deleted' etc. There will be a another update soon which backs out of these changes. Hopefully all of them. These are links to the bug reports which mentions the backout: https://bugzilla.mozilla.org/show_bug.cgi?id=2001557 https://bugzilla.mozilla.org/show_bug.cgi?id=1993842