You can use a custom style rule to change the color. Custom style rules can be applied to the user interface either using the Stylish extension or by creating a file named userChrome.css in your profile (settings) folder. To create the rule, though, I think someone might need to see the particular shade of green. I don't know whether it is possible to detect that automatically. Alternately, you could make the background of the address bar transparent so the color behind it shows through. There's an example of that kind of rule in this thread: [https://support.mozilla.org/questions/1000123]. If that looks too naked, one might try a translucent background (e.g., white, but only 10% opaque so most of the background color shows through).