In browse mode (also called virtual cursor mode), a screen reader intercepts keystrokes to let users navigate by heading, link, or landmark rather than sending every key press to the page. Focus mode hands keystrokes directly to the page, which is necessary inside text fields, comboboxes, and custom widgets where the user needs to type or use arrow keys for the widget’s own behavior.
Screen readers usually switch modes automatically based on ARIA roles, but a custom widget with incorrect or missing roles can leave a user stuck in the wrong mode, unable to either read the content or interact with the control properly.