Yes, the URL has been moved to the side in Firefox 48. It is a little hard to get used to moving my eyes over there. I doubt there is a built-in setting to change it, but maybe another volunteer knows of one. Many aspects of Firefox can be modified using custom style rules, while in other cases, a dedicated add-on is needed. I searched around and didn't see one for this yet, but I imagine a lot of creativity will be brought to bear in the next week or so, so stay tuned.