The console reports:
Error in parsing value for ‘left’. Declaration dropped.
Error in parsing value for ‘top’. Declaration dropped.
A little debugging shows that a NaN is getting into the item properties and then propagating through the calculations until it gets to the style.left= line where it fails, preventing the item from moving.
Resizing the window will make everything start working.
I see. I have some ideas what it could be. But since no Win10+FF combination I tried shows this behaviour, it's hard to debug. If you like, shoot me an email. Maybe we find a bug in the Win10 preview or Firefox.
A little debugging shows that a NaN is getting into the item properties and then propagating through the calculations until it gets to the style.left= line where it fails, preventing the item from moving.
Resizing the window will make everything start working.