Fix
On ultrawide and 4K monitors the URL bar expanded to a disproportionate width. Its size used viewport-relative units (vw), which scale linearly with screen width, so a bar sized right at 1080p stretched across half a 3440px or 4K display. FoxOne now caps the URL bar at a fixed pixel ceiling (about 630px at rest, 900px on focus) while keeping the proportional sizing on smaller screens, so it stops growing past a sensible point regardless of monitor size.
Thanks to Metalwell for the report.