The Opened folders section and its use is described in the manual.
You can view the opened folders in the section where individual items in the table are used as follows:
Name of the user folder following the ~user_name@domain/folder name pattern
All users whose folder is currently opened are involved. Multiple users can be listed in case of public or shared folders.
Total number of users whose folder is currently opened. Multiple users can be listed in case of public or shared folders. It is also possible that a folder is opened more than once by a user.
This item informs if the index.fld file has been uploaded by the server. This file allows various additional information display properly (flags, read-unread information, etc.).
You can use the button to manually refresh the page listing open folders.