How to resize Safari address bar on macOS Sierra or newer?

Solution 1:

  1. Right-click on an empty area at the top of Safari’s window and select Customize Toolbar.
  2. You’ll see two “flexible spaces” on each side of the URL bar. 2 tranparent boxes.
  3. Remove these boxes (by dragging them out of the toolbar), and you should wind up with a larger URL entry area.