Any browser on a page allows to increase font size with Zoom in/out options convenient for users with bad eyesight problems, why font size of URL in address bar should be that small? can’t that be adjusted yep! but without much knowing of CSS with Firefox extension called Make address bar Font Size bigger which makes the URL address bar font size bigger.
This extension even makes the autocomplete suggestions dropdown that appear when you start typing on address bar even bigger which add more comfort to the user. If you’re on a LCD screen with high screen resolution you don’t need to bend to get the sight of web address. You can use the toggle button that appears on left of the address bar to increase/decrease font size.
You can also easily know while visiting shopping sites whether you’re on a trusted site or the site that phishing you like that one by looking at the big URL, that does make the difference IMO.