I wonder if you would consider tweaking the code to make it more compatible with the Opera 20+ branch. The extension works "fine" in opera, but with only two exceptions. With Opera, it does not respect the target width setting for the sidebar. Each time Opera is restored from the taskbar, Sidewise doubles in width, running off the side of the screen. Second issue is more minor, in that Sidewise has an unexpected and non-working address bar at the top.
Customer support service by UserEcho