Clicking Next Unread finds the next unread in any folder, but Previous Unread doesn't
When reading messages, clicking the Next Unread will go to the next unread message, whether it is in the same folder or not. It will progress down the list of folders, until none are found.
Clicking the Previous Unread cannot go beyond the top of the current folder.
Also, switching to a new folder with Next Unread requires 2 operations. One leaves the currently open message, and the next is required to switch to the folder containing the next unread message.
Wšykne wótegrona (3)
Use keyboard shortcuts. https://support.mozilla.org/en-US/kb/keyboard-shortcuts
Identical behavior with keyboard shortcuts...
It works here. Try to start Thunderbird in safe mode. https://support.mozilla.org/kb/safe-mode-thunderbird