Section 508 Accessibility Guideline 2.1 says all functionality should be available from a keyboard.
https://www.w3.org/TR/2008/REC-WCAG20-20081211/#keyboard-operation

However, when the mode bar is displayed, there is no way to tab into it and to tab between buttons on the mode bar. This needs to be added.