In Firefox 52 Touch events where re-enabled, which seems to cause a lot of trouble in ExtJS 5.
The most annoying exampel is that you can't open a combobox list.

STR: On a laptop with touchscreen (or modifying source to have Ext.supports.TouchEvents returning true) open and try to open the combobox by clicking on the arrow.

Expected result : The list open
Actual result: The list does not open

I can spot several Ext.isWebkit tests along those on supports.TouchEvent , and I think one of them in Ext.event.publisher.Gesture might be the root of the issue :

if (!handledDomEvents.length || (supportsTouchEvents && Ext.isWebKit && {
  handledDomEvents.push('mousedown', 'mousemove', 'mouseup');

Because if you don't add those, only the touch events are handled. So if you're on your touch-capable laptop, but using a mouse, you can't interact with anything.