(Hidden by Administrator)
Bug 1829737 Comment 2 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
There's also the other more brute-force approach which is to open the [config editor](https://support.mozilla.org/en-US/kb/config-editor) from the settings and set `mailnews.default_view_flags` to 0. That will make every folder unthreaded by default.