Close Button Minimizes the Browser to System Tray
I've encountered a lot of Windows app for this (not sure with Mac) wherein there's a checkbox option for sending the application to the system tray when you press the 'X' to close the window. What I have in mind is that, it will hibernate all tabs (or as an option, terminate all tabs) when you do it, thus saving some RAM. One big purpose why I would love to see this is because, relaunching the browser takes some time. Sometimes I close the browser, then I would remember that I need to search google for something, so I have to relaunch it again, and I have to wait for the browser to load everything again. This feature, I believe, will do the trick. A keyboard shortcut to relaunch Vivaldi from system tray would be awesome too.
Set a shortcut in Settings, Keyboard, Window, Minimise.
I use TrayIt! for this. You can press the minimize button on every window and hold the shift key and that window will be minimized to the system tray. It also can be configured to always minimize some window to the tray.
However, it would be nice if this functionality was built into Vivaldi. Then I would not need a separate application.