On the main browser window, you can access and modify
chrome://browser/content/browser.xul
using the DOM Inspector and adjusting it in the profiles' userChrome.css
file.
I am interested in doing something similar for the tab group window (CTRL+SHIFT+E), but I haven't been able to find any information on how to open it in a tab or access the DOM in any other way.
Has anyone attempted this before? Is it possible to achieve it this way, or would I need to delve into more complex methods?