User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:94.0) Gecko/20100101 Firefox/94.0

Steps to reproduce:

In the jQuery UI's Dialog widget, when the Close button has focus, the blue rectangle representing said focus is drawn incorrectly. Its left border is shifted way to the left.

To see the effect, simply visit https://jqueryui.com/dialog/
Screenshot attached.

If you don't see it straight away, click the white field around the dialog and then press Tab once so that the keyboard focus moves to the Close button.

Other major browsers do not demonstrate this behaviour. Older Firefox versions don't demonstrate it either.
Firefox 94 demonstrates it on both Windows 10 and Windows 7.