On some pages (e.g., login) one form field is automatically "focused" when the page is loaded. That is, the cursor is placed in that field just as if the user had selected it. Screen readers read this form field immediately, without starting at the beginning of the page.
In 2006 the Open University's accessibility study pinpointed this issue:
"The automatic placing of the cursor in the 'username' field is useful for sighted users (including dyslexic, partially sighted, hearing impaired etc.) who will see that it is there, but for screen readers this can be difficult because the screen reader focus does not start at the top of the page and will miss any instructional text such as 'Login here using your username and password.' It is difficult to know how to resolve this conflict of needs and so this requires further consideration."
Why it matters
This is one of very few accessibility problems in Moodle that caused total failure for a screen reader user. Other problems caused or contributed to wasted time or lack of understanding, but did not cause a user to give up entirely.
Vision-impaired users had no trouble with this feature. While I'm sure that the Open University's concern about dyslexic users is valid, the focus of this study is blind and vision-impaired users. For blind users I think the conclusion is clear: automatic focusing of form fields is harmful.
No form fields should be focused automatically. This change will reduce convenience for sighted users but will not prevent them from accomplishing tasks. It is a good candidate for a user preference, but this preference should be off by default.