Pressing tab repeatedly in the search widgets in the gradebook report pages has a different outcome in Firefox and Chrome.
For example, in the User report in gradebook, if the list of available items in he widget is longer and triggers the scroll, when tabbing through the elements the following focus is applied

Chrome:

1. search input
2. 'All users' option

Firefox:

1. search inpit
2. user list container element
3. 'All users' option