I'm very happy to see that Vivaldi will have the good old panel back. Currently, I cannot add a custom panel I have very good reasons for using own 'panels' in the sidebar: - As I'm using my bookmarks cross browser, cross platform and cross devices, I'm using an online bookmark manager (sitebar). It makes no sense to duplicate the bookmarks on a local machine or for a proprietary service (like Firefox Sync, Google or even Opera Sync). - When I was a web developer, ASCII- and UTF8 character tables were very good to have them reachable. I found the panel/sidebar very handy and would like to have a customizable panel where I can insert ANY url into it.