Event accuracy improvements, bugfixes around tabbing focus

Improvements to the mouse event accuracy for mouseover and mousemove events (and the related pointerevent and touchevents respectively), including special nuances for firefox and chrome behaviors.

Lots of new tests and testpoints were added to lock down these changes.

Fixed a bug with tab and anti-tab where index out of range exceptions were occurring at the top and bottom of the page.

Upgraded Firefox version to ensure compliance with new Firefox behaviors.