How can I modify the new Australis UI with userChrome.css?

Question

With a non-dark theme it looks ok, but these gradients make me want to use another browswer. I'll stay away from Idiocracy jokes about how "simple" the new menu is.
I don't want to use a classic theme restorer to go back to the way it looked before. I would like to move forward, and create a new personalized interface.
Can someone create a wiki on the different elements of the browser interface?
IMO you will save quite a few power users from migrating to something truly "customizable" (no moving buttons around doesn't count (haven't we always been able to do that?))

Answer 1

The DOM Inspector (DOMi) has a menu item (Edit > Select Element By Click) and a toolbar button "Find a node to inspect by clicking on it" (left icon on the toolbar in the DOMi).
* open the browser window in the DOMi (File > Inspect <b>Chrome</b> Document) and choose the first entry from the drop-down list.
* click the "Find a node to inspect by clicking on it" button and use the keyboard (Alt Tab) or the Task bar to go back to the browser window (do not click in the browser window other than the title bar).
* click that element with the mouse and keep the button pressed until you see a red border to indicate the the DOMi has located that element in the DOM tree.
*DOM Inspector: https://addons.mozilla.org/firefox/addon/dom-inspector-6622/
*https://developer.mozilla.org/Introduction_to_DOM_Inspector
*https://developer.mozilla.org/DOM_Inspector