For many years I used the Stylish addon to alter the font in my URL bar (specifically to make it a fixed-width font). Stylish will no longer work once FF 57 comes out, so I switched to Stylus, but the same style rule (#urlbar { etc }) no longer does anything. I’m assuming that something about addons has changed to prevent them from altering the DOM of the Firefox UI itself, so I thought maybe there’s some way to do that with themes; but the theme documentation (which is extremely scanty) indicates no such way to do this. So the question is:
Is there any way to use a theme or addon or other functionality to modify the URL bar font in Firefox? I’m a web developer so if I have to write my own theme or addon I will.