Developer Tools Always Opens In A New Window
Having the developer tools open in a new windows with no option to have it be apart of the browser window can be very challenging. It would be appreciated if you could add the options back in so it appears at the bottom or on the right side of the browser window.
Looks like you are talking about "docking" developer tools. This has been asked for over a hundred times by now…
This is not something that can be "added back in," because it is a feature of the Chrome interface operating on the Chromium engine. Vivaldi does not use the Chrome interface or any part of it, but rather a UI written in completely different technologies.
So in order to create the ability for developer tools to be docked in the Vivaldi window, a bunch more code has to be written to create that effect. So many people have asked for it that I feel pretty certain Vivaldi will do all of the coding necessary to accomplish it. But I wouldn't care to predict how long that might take...