It does perfectly what I want it to do: to show in which folder a bookmark is. However, on install, it opens itself in every window (and replaces Tree Style Tab), where we have to close it or switch back. It would be better to open it only in the active window or none at all if that's not doable.
Hello Thomas, correct, this is the default behavior of FF -> https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/sidebar_action
This is a security default, so that an install doesn't go unnoticed by the user.
Note that: - If you immediately redisplay the previous sidebar you had, then subsequent new windows use the one you just selected. - When you close FF with a sidebar open, next time it restarts, it reopens with the same sidebar you had at time of close. These are FF behaviors at this time which an add-on cannot modify.