Crome is 45.0.2454.94 (very new) and Firefox is fennet 41.0 (20150917151118)
I did some research and found that this problem depends on combinations of at least “chartContainer height” and “legend fontSize”. http://ru-stad.name/plot/plot6.htm works in Crome but not Firefox as it is now but not for many other variable combinations. Could it be that the legend is somehow marginally placed outside a clickable area or behind something? If I replace itemclick with itemmouseover it always works as expected for mouseover however.
Crome, Firefox and Opera fails, both on Samsung tablet and phone.
The Samsung browser is a bit better on the phone but not on the tablet.
Clicking on curve points works perfectly for all browsers.