Consider adding a Sidebar from the Pulse Browser source code

Pulse Browser is a Firefox fork focused on minimalism and usability. They developed a very convenient sidebar which would be great for Librewolf. you can see the sidebar on their website https://pulsebrowser.app

and the source code to the sidebar is here https://github.com/pulse-browser/browser/blob/alpha/src/browser/base/content/browser-sidebar-js.patch and https://github.com/pulse-browser/browser/blob/alpha/src/browser/base/content/browser-box-inc-xhtml.patch