Story tool: Mouse-clicking on add block buttons does not move focus in Firefox

Mouse-clicking on any of the add block buttons does not move focus to the selected button, such that subsequently selecting the tab key continues the focus order from the last-focused item. This is not the case when mouse-clicking on any item other than the add-block buttons, and does not occur in Safari or Chrome. Note that mouse-clicking on the add block buttons disappears the visible focus frame from its current location.