Firefox/Chrome both do it for me, on the three different computers I use. The charts/orders seem to update in real time, and without lag. Just that cross hair. I wasn't sure if it was a plotting tool or had some other use.
Well, the crosshair is a way to see the time of the candle and the exact price / volume at the hover point.
That is very odd that you're having the same problem on multiple computers. I am looking into further chart customizations, and crosshair will definitely be on the list of options.