When I open the developer tools I get the familiar tools, but they are in their own window.
How can I dock them to the bottom of the window?
It's possible since Vivaldi snapshot 1.10:
https://vivaldi.com/blog/snapshots/docked-developer-tools-vivaldi-browser-snapshot-1-10-829-3/
Docked Developer Tools We have had a long standing request for the ability to dock Developer Tools. Well, wait no longer, we are introducing this handy feature in our very first 1.10 snapshot. All of you developers who desperately wanted this, can now breathe a sigh of relief. Of course, if you prefer them undocked, that still works too!