I evaluated several versions of Firefox, my conclusion is that the drop down menu doesn't ship with Firefox version 54.0.1 and earlier but ships with version 55.0 and later. So there's no reason to rewrite Sidebars List as a WebExtension as required by Firefox 57.
I evaluated several versions of Firefox, my conclusion is that the drop down menu doesn't ship with Firefox version 54.0.1 and earlier but ships with version 55.0 and later. So there's no reason to rewrite Sidebars List as a WebExtension as required by Firefox 57.
Can you please state this at https://addons.mozilla.org/en-US/firefox/addon/sidebars-list/ ?