I know what you mean put I mean lets use this example..
Lets say I'm on a webpage and some feature of the browser doesn't work on the site
How it is now so A
A ) I go to menus and then find & click feedback. Then I get another page as an active tab. While filling it I require more information from the page I was on which might be one of the 50 tabs or so.. So I need to find it. Once I do, I open a notepad and type any information there so I can just use it on the side once I go back to that feedback page. That's how it's now for me if I have that many tabs open.
What I suggested so B
B ) I go to menus and then find & click feedback. Then I start filling that popup(I don't mean webpage popup but some UI based popup with form slots to fill) and notice I require some information from the page so I move the window a bit to the right and keep on filling from the site.. Or just close it, type information from the page that is still open to a notepad, go back to feedback and then fill it with that.
Perhaps I'm just too used to reporting bugs and suggestions with Windows 10 Insider Preview(been in it from before Win10 was released) within the OS. I don't know anything about opera code but of course it could be possible it doesn't even support UI popups. About and Update Check links from the menus open just pages in tabs too but with them I wouldn't even feel the need to have the page open when I've gone there. EDIT: Actually now that I think about it might just drag the tab where some feature bugs to my second monitor and after that go to report it so I have the page on the second screen but not all have a setup like that.