To use the Advanced Unread Folders extension for Firefox just install and then select the Unread (Hierarchy) view with the arrows above the folder pane.
This add-on's options (Tools > Addons > Advanced Unread Folders > Preferences) allow you to select folders that should always be shown, regardless of if they contain unread folders or not. By default this is set for inbox, templates and favorite folders.
If you'd only like to show special folders (like Drafts or Templates) for certain accounts, I'd suggest marking them as favorite folders and then only enabling the option to always show favorite folders.
· Mozilla Firefox
What's New in This Release: [ read full changelog ]
· This version fixes a few small style issues from the AMO review and also a bug where the view is not loaded at Thunderbird startup.