This is related to T69153: VisualEditor: Tab order or behavior is bad in the Save dialog, but specific to Chrome/Safari:
Whatever the dialog box, once you've tabbed through whatever links and buttons are inside that dialog (and on the tab list, which isn't always all of them), then pressing tab takes you outside the dialog box to these items:
- the browser's URL bar
- the main Wikipedia search box
- the Cancel button (on VisualEditor's toolbar)
- the Save button (on VisualEditor's toolbar)
- the top of the article
- the slug at the top of the article, where it gets stuck forever.
and never lets you get back to the dialog box. This means that if you press tab one time more than you meant to, you cannot use or close the dialog box without taking your hands off the keyboard.