What does your feature entail? What is it for? How will it affect existing workflows or user experience?
In Firefox and Chrome, you are able to edit the CSS of the browser to change the look and feel of the browser. See Modern Modoki for firefox. It would be nice if people could edit the CSS of Orion to make it work best for them.
What are the exact ways that you see a user using your proposed feature? Please go into as much detail as possible, and provide examples of how other browsers/apps implement this feature, if applicable. If your feature suggestion adds on to an existing feature, how would it work into it to extend its usefulness?
I would see users perhaps making the browser look and feel more native to Mac OS than it already is. Either that or making fun CSS projects that make the browser look totally different.