I mean, for example, not everyone uses ubuntu's overlay scrollbar in elementary os. Personally, I hate them, and I use these thin grey elementary scrollbars.
Also, I recently changed my system theme to Milk + harvey window tops and I would KILL to get a milk firefox elementary theme. If you are not willing to make one, is there a way for me to modify yours and send it for you to upload here? I would find some free time for that ;)