${HOME}/.thunderbird

 ${HOME}/data/_.thunderbird

 .thunderbird → ./data/_.thunderbird

- Brief technical introduction: Using Linux I did move directory: ${HOME}/.thunderbird towards: ${HOME}/data/_.thunderbird creating a symbolic link in the filesystem: .thunderbird → ./data/_.thunderbird The logic was to contain all meaningful program user data in one parent directory data that can be moved between multiple machines. After years did eventually change operating systems. I perceived issues with symbolic links. So I returned directories to the original path. This means: remove the symbolic link and copy the directory within the expected path: "${HOME}/.thunderbird". This was done in combination with thunderbird upgrade version 45 to 52. I kept the old directory available to rollback if a severe error was detected. - Problem seen: After previous changes thunderbird worked without any perceived issues. After much time passed cleansing was done to remove the previous installation data directory: "${HOME}/data/_.thunderbird". The problem seen is that removing the old installation affects thunderbird. The new upgraded version show profile data is lost: News-RSS-Feed, localhost offline mail folder [without online account]. My investigation showed thunderbird somehow uses two directories at the same time. Some data is writen in the good directory (relative path), some in the old directory. This means my program need both directories to preserve all data. This might be due to some thunderbird components not really using a relative path. As the past use of a symbolic link could gravely confuse and affect a component. So even if the profile directory is copied to a new location, the old path is mysteriously preserved and being partially used [for some data]. My request is for technical feedback from an expert. To understand how that could happen. To comprehend how some profile internal data is being stored outside the relative path. Wish to fix the problem and consolidate both directories into one. Might also affect thunderbird as a bugfix; because the use of a symbolic should not affect in this way.